Agent Transfer Protocol (AGTP)

Agent Transfer Protocol (AGTP) Nomotic, Inc.

chris@nomotic.ai https://nomotic.ai

Applications and Real-Time Independent Submission AI agents agentic systems protocol agent traffic agent transfer AI agents and agentic systems generate a growing volume of intent-driven, unstructured, and undifferentiated traffic that flows through HTTP indistinguishably from human-initiated requests. HTTP lacks the semantic vocabulary, observability primitives, and identity mechanisms required by agent systems operating at scale. Existing protocols described as Agent Group Messaging Protocols (AGMP), including MCP, ACP, A2A, and ANP, are messaging-layer constructs that presuppose HTTP as their transport. They do not address the underlying transport problem. This document defines the Agent Transfer Protocol (AGTP): a dedicated application-layer protocol for AI agent traffic. Version 05 restores the canonical Agent-ID as the primary identity primitive and decouples Trust Tier 1 verification from DNS as a sole requirement. A canonical Agent-ID is derived from the agent's Birth Certificate hash and is authoritative in every AGTP protocol operation. Three equivalent verification paths are recognized for Trust Tier 1: DNS-anchored verification via RFC 8555 ACME challenge, log-anchored verification via Birth Certificate inclusion in an append-only transparency log aligned with RFC 9162 and RFC 9943 (SCITT), and hybrid verification combining DNS control with blockchain address ownership. The .agent and .nomo hierarchical namespaces are reinstated as agent-native resolution aliases with deterministic disambiguation rules governing coexistence with Web3 naming systems. Version 04 introduced normative integration hooks for the AGTP Merchant Identity and Agentic Commerce Binding specification , which defines the merchant-side identity model that complements AGTP's agent-side identity model. Version 04 added four merchant-related request headers (Merchant-ID, Merchant-Manifest-Fingerprint, Intent-Assertion, Cart- Digest), the 455 Counterparty Unverified status code, and the merchant and intent Authority-Scope domains. Together these elements close the verification loop between the initiating agent and the receiving merchant on AGTP PURCHASE invocations. Version 03 introduced normative integration with the Agentic Grammar and Interface Specification (AGIS) , which defines the grammar-based validation pathway for AGTP method identifiers. AGIS-conformant methods are accepted at the transport layer via the Method-Grammar header without requiring prior IANA registration, enabling organizations to define domain-specific Agentive API vocabularies while preserving interoperability through shared grammatical constraints. AGTP provides agent-native intent methods (QUERY, SUMMARIZE, BOOK, SCHEDULE, LEARN, DELEGATE, COLLABORATE, CONFIRM, ESCALATE, NOTIFY, DESCRIBE, SUSPEND), protocol-level agent identity and authority headers, and a status code vocabulary designed for the conditions AI agent systems encounter. AGTP SHOULD prefer QUIC for new implementations and MUST support TCP/TLS for compatibility and fallback. It is designed to be composable with existing agent frameworks, not to replace them. Version 02 introduces capability discovery (DESCRIBE), resource budget signaling and enforcement, optional RATS-aligned execution attestation, observability hooks, network zone isolation, session suspension as a method, and normative composition profiles with AGMP (Agent Group Messaging Protocols). Version 02 enables dynamic capability negotiation and resource-aware governance.

Introduction Note Regarding Intellectual Property: Implementers should be aware that extensions and certain mechanisms referenced in this document -- including the Agent Certificate extension (Section 7.2), the ACTIVATE method, the Agent Birth Certificate mechanism (Section 5.7), and the .agent and .nomo file format specifications (Section 2) -- may be subject to pending patent applications by the author. The core AGTP specification is intended for open implementation without royalty obligation. The licensor is prepared to grant a royalty-free license to implementers consistent with . IPR disclosures: https://datatracker.ietf.org/ipr/ -- see also Section 7.7.

Background The deployment of AI agents and multi-agent systems is accelerating across enterprise, research, and consumer contexts. These systems execute complex, multi-step workflows, querying data sources, booking resources, delegating subtasks to peer agents, and escalating decisions to human principals, with minimal or no human supervision per transaction. Unlike human-initiated web traffic, agent-generated traffic is dynamic, high-frequency, intent-driven, and often stateful across sequences of related requests. The infrastructure carrying this traffic was not designed with these properties in mind.

Limitations of HTTP for Agent Traffic HTTP has served as the internet's primary application-layer transport for over three decades. Its evolution through HTTP/2 and HTTP/3 has improved performance, multiplexing, and latency. However, the fundamental model of HTTP being stateless, resource-oriented, human-initiated request/response, creates specific failures when applied to agentic systems at scale:

Traffic indistinguishability: Agent-generated requests are structurally identical to human-initiated requests at the transport layer. Operators cannot identify, route, or govern agent traffic without application-layer instrumentation.
Method vocabulary mismatch: HTTP's method set (GET, POST, PUT, DELETE, PATCH) describes resource operations. Agent traffic expresses purposeful intent, summarize, book, delegate, escalate. The mismatch forces intent into request bodies, invisible to protocol-level handlers.
Identity and attribution absence: HTTP carries no native mechanism for asserting agent identity, declared authority scope, or the principal accountable for an agent's actions.
Session semantics mismatch: HTTP's stateless model is optimized for isolated request/response cycles. Agent workflows are inherently stateful sequences.

Why Not Evolve HTTP? A natural question is whether these limitations could be addressed by extending HTTP rather than defining a new protocol. There are three specific reasons why HTTP extension is not the preferred path. First, the HTTP method registry is effectively frozen for new semantics. defines the HTTP method registry with IETF Review as the registration procedure, meaning new methods require a full IETF consensus process and must be backward-compatible with existing HTTP implementations. Adding intent-based verbs (SUMMARIZE, DELEGATE, ESCALATE) to HTTP would require every HTTP client, server, proxy, and middleware component to ignore or handle unknown methods gracefully, a compatibility constraint that limits how agent-specific semantics can be expressed at the protocol level. Second, HTTP carries decades of backward-compatibility constraints. Features such as persistent agent identity headers, authority scope declarations, and session-level governance semantics would require HTTP extensions that interact unpredictably with existing caching, proxy, and CDN behavior designed for human-generated traffic patterns. Third, the observability goal making agent traffic distinguishable from human traffic at the infrastructure layer cannot be achieved by adding fields to HTTP. Infrastructure components route and filter HTTP traffic based on methods and headers that are identical across agent and human requests. A protocol-level separation is necessary to give infrastructure the signal it needs. AGTP is therefore designed as a dedicated protocol rather than an HTTP extension. HTTP and AGTP coexist: human traffic continues to flow over HTTP; agent traffic flows over AGTP. The two protocols serve different classes of network participant. Note: The abbreviation AGTP is used in this document to distinguish the Agent Transfer Protocol from the Authenticated Transfer Protocol (ATP) working group currently chartered within the IETF. The URI agtp:// is proposed for IANA registration as a new and distinct scheme.

Motivation for a Dedicated Protocol These limitations are architectural, not implementational. They cannot be resolved by better middleware or application code layered on HTTP. They require a protocol designed from first principles for AI agent systems. AGTP is that protocol. It provides a dedicated transport environment for agent traffic with: native intent-based methods, mandatory agent identity headers, protocol-level authority scope declaration, and a status code vocabulary for the conditions AI systems encounter.

Scope and Target Audience This document covers AGTP architecture, design principles, stack position, request and response header format, agent-native method definitions and semantics, status code vocabulary, security considerations, and IANA considerations. The Agent Certificate extension for cryptographic binding of agent identity to AGTP header fields is described at a high level in Section 7.2. Full specification is provided in a separate companion document: . That extension may be subject to pending intellectual property claims; see Section 7.7 and the IPR Notice preceding the Abstract. Merchant-side identity verification for PURCHASE counterparties is described at a high level in Section 8 of this document and specified in full in a separate companion: . This document registers the merchant-related request headers, the 455 Counterparty Unverified status code, and the merchant and intent Authority-Scope domains; the Merchant Manifest Document, Merchant Birth Certificate, counterparty verification procedure, and Intent Assertion JWT format are specified in the companion. Target audience: AI agent developers, protocol designers, cloud and network infrastructure providers, enterprise security and compliance architects, and standards community participants.

AGTP as the Transport Foundation for Agent Group Messaging Protocols AGTP is the purpose-built transport and governance layer for Agent Group Messaging Protocols (AGMPs): the category of higher-layer AI agent messaging standards that includes the Model Context Protocol (MCP) , the Agent-to-Agent Protocol (A2A) , the Agent Communication Protocol (ACP) , and emerging others. AGMPs define what agents say. AGTP defines how those messages move, who sent them, and under what authority. AGTP provides the narrow-waist foundation that AGMPs inherit without modification: intent-native methods, mandatory agent identity and scoping, resource budget enforcement, observability hooks, and normative composition profiles. A deployment running any AGMP over AGTP gains transport-level governance without changes to the messaging layer. The AGMP category term is introduced in this document to provide a stable collective reference for the class of protocols that AGTP serves as substrate. It is not a formal IETF term of art; it is a descriptive classification. Individual AGMP specifications retain their own names and development paths. AGTP does not govern, modify, or supersede any AGMP.

AGTP as Substrate for AGMPs

Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals.

Agent:: An AI software system that executes tasks, makes decisions, and takes actions without continuous human supervision per transaction.
Principal:: The human, organization, or system that authorized an agent to act and is accountable for its actions.
Agent-ID:: A unique identifier for a specific agent instance, present in all AGTP request headers.
Principal-ID:: The identifier of the principal on whose behalf an agent operates.
Authority-Scope:: A declared set of permissions defining what actions an agent is authorized to take, in the format domain:action or domain:*.
Intent Method:: An AGTP method name expressing the agent's purpose, as distinguished from HTTP resource-operation verbs.
Delegation Chain:: An ordered record of Agent-IDs representing the sequence of delegations that produced the current request.
Escalation:: An agent's intentional deferral of a decision or action to a human principal or higher-authority agent.
Attribution Record:: A logged record of an agent action sufficient for audit and compliance purposes.
Session:: An AGTP persistent connection context shared across multiple method invocations within a single agent workflow.
SEP (Scope-Enforcement Point):: An AGTP-aware infrastructure component, load balancer, gateway, and proxy, that enforces Authority-Scope compliance without application-layer access. Requires the Agent Certificate extension ().
Agent Package (.agent):: A portable, open deployment artifact for an AI agent. An .agent file contains an embedded Agent Manifest, an integrity hash covering all package contents, and a behavioral trust score computed at packaging time. The .agent format is an open specification. It is analogous to a container image: a self-describing, portable unit of deployment. The .agent suffix is a file format designator and MUST NOT appear as a hostname component or top-level label in agtp:// URIs. Note: the .agent file format specification may be subject to pending patent claims by the author; see Section 7.7.
Governed Agent Package (.nomo):: A deployment artifact in the .nomo format, which extends the .agent format with a CA-signed certificate chain binding the package to a verified governance zone and issuing principal. The .nomo format is to .agent as HTTPS is to HTTP: the same structural foundation with an added layer of cryptographic trust. A .nomo package is required for agents operating at Trust Tier 1 (see Section 5.2). The .nomo suffix is a file format designator and MUST NOT appear as a hostname component in agtp:// URIs. The name derives from the Greek nomos (νόμος), meaning law, rule, or governance, the same root that underlies autonomy (self-law), nomocracy (rule of law), and onomastics. A .nomo package is literally an agent operating under law: its behavior is bounded by a cryptographically enforced governance context at the packaging layer. Note: the .nomo file format specification may be subject to pending patent claims by the author; see Section 7.7.
Agent Transfer Document (.agtp):: The wire-level manifest document format defined by this specification. An .agtp document is a signed JSON structure containing the fields defined in Section 5.5 (Agent Manifest Document). It is the output format returned by all AGTP URI resolution requests. Both .agent and .nomo packages produce .agtp documents when queried; the .agtp format is the protocol's canonical representation of agent identity and is independent of the underlying packaging format. The .agtp suffix MAY appear in filenames for stored manifest documents but MUST NOT appear in agtp:// URIs. The Content-Type for .agtp documents is application/agtp+json.
URI (AGTP):: An agtp:// scheme URI that identifies an agent or agent namespace. AGTP URIs are addresses, not filenames. File extensions (.agent, .nomo, .agtp) MUST NOT appear in canonical AGTP URIs. See Section 5.1 for the canonical URI forms and resolution semantics.
Agent Namespace Document:: A cryptographically signed application/agtp+json document returned in response to a request targeting an organization's agent registry root (e.g., agtp://acme.tld/agents). Lists all Active agents registered under the organization's governance zone. The document is generated and re-signed by the governance platform on any registry change. It is not a manually editable file. See Section 5.4.
Agent Manifest Document:: A cryptographically signed application/agtp+json document returned in response to a request targeting a specific agent (e.g., agtp://acme.tld/agents/customer-service). Contains the agent's birth certificate fields, lifecycle state, behavioral trust score, authority scope categories, supported methods, and governance zone. Derived directly from the agent's .agent or .nomo package; the package integrity hash is verified before the manifest is served. See Section 5.5.
Agent Birth Certificate:: A cryptographically signed identity document issued to an agent at registration time by a governance platform. The Birth Certificate is the genesis record of an agent's existence: it establishes the agent's identity, ownership, authorized scope, behavioral archetype, and governance zone before the agent takes any action. Authority is issued through the Birth Certificate; it is never self-assumed. The Birth Certificate is the source document from which the Agent Manifest Document (Section 5.5) is derived when an AGTP URI is resolved. The certificate_hash field of the Birth Certificate is the basis for the agent's canonical Agent-ID. In this sense the Birth Certificate functions as the agent's social security number: issued once at creation, permanently bound to the individual, and the authoritative identity record from which all other identity representations derive. Birth Certificate fields map directly to AGTP protocol headers: agent_id maps to the Agent-ID header; owner maps to the Principal-ID header; scope maps to the Authority-Scope header. See Section 5.7. Anonymous agents are ungovernable. Without a Birth Certificate, there is no mechanism to trace decisions to a responsible principal, enforce scope boundaries, or maintain a meaningful audit trail. Note: the Agent Birth Certificate mechanism may be subject to pending patent claims by the author; see Section 7.7.
Governance Token:: A signed, time-limited JWT artifact issued by a governance runtime that encodes a specific governance decision for a specific action. Governance tokens are the runtime companion to the static Birth Certificate: where the Birth Certificate establishes persistent identity, the Governance Token carries a bounded authorization for a single action or session. Tokens carry the governance verdict (ALLOW, DENY), the agent ID, action details, trust score dimensions, issuer identity, and expiry. Default TTL: 30 seconds. Tokens MUST NOT be reused across actions; each action requires a fresh evaluation and a fresh token.
Trust Tier:: A classification assigned to an agent based on the strength of identity verification backing its registration. Tier 1 (Verified): org anchor is a real DNS domain with confirmed ownership and a .nomo governed package. Tier 2 (Org-Asserted): org label is present but DNS ownership is unverified; .agent package acceptable. Tier 3 (Experimental): X- prefix required; not discoverable through the public AGTP registry. See Section 5.2.
AGMP (Agent Group Messaging Protocol):: The collective term for higher-layer AI agent messaging standards that operate over AGTP as their transport substrate, including MCP , A2A , ACP , and ANP . AGMPs define what agents say to each other. AGTP defines how those messages move. The term is introduced in this document as a descriptive classification; it is not a formal IETF term of art.
DESCRIBE:: An AGTP Tier 1 core method that returns the declared capabilities, supported modalities, method vocabulary, and versioned feature set of a specific agent endpoint. Distinguished from URI resolution (which returns identity) by returning operational capability metadata suitable for pre-task negotiation. If the capability_domains parameter is omitted, the server SHOULD return all supported domains. Category: ACQUIRE.
SUSPEND (method):: An AGTP Tier 1 core method that places a specific active session workflow into a recoverable paused state, issuing a resumption nonce for re-entry. Distinguished from the lifecycle SUSPEND event (Section 6.7.6): method-level SUSPEND is session-scoped and does not affect the agent's registry lifecycle state or Birth Certificate validity. Category: ORCHESTRATE.
Budget-Limit:: A request header declaring the maximum resource consumption the principal authorizes for a method invocation, expressed as space-separated unit:value tokens drawn from the IANA AGTP Budget Unit Registry. Example: Budget-Limit: tokens=5000 compute-seconds=120 financial=10.00USD ttl=3600. Exceeding the declared limit MUST cause the server to return 452 Budget Exceeded rather than continue execution. Note: ttl= is RECOMMENDED to bound budget lifetime.
AGTP-Zone-ID:: A request header declaring the network zone or organizational boundary within which a request must be processed. Scope-Enforcement Points (SEPs) MUST enforce zone boundaries and MUST return 453 Zone Violation if a DELEGATE or COLLABORATE request would route outside the declared zone.

Problem Statement AGTP is motivated by three distinct, compounding failures in how current internet infrastructure handles AI agent traffic.

Problem 1: Undifferentiated Agent Traffic on HTTP AI agents generate intent-driven, structured traffic that is functionally invisible to the infrastructure it traverses. This traffic flows through HTTP alongside human traffic with no protocol-level differentiation. Observability failure, routing inefficiency, and security blindness result, operators cannot determine what fraction of traffic is agent-generated without application-layer instrumentation that is expensive, inconsistent, and easy to circumvent. AGTP response: a dedicated protocol environment for agent traffic. Infrastructure can distinguish, route, monitor, and govern agent traffic natively.

Problem 2: Semantic Mismatch Between Agent Intent and Available Methods AI agents operate on intent. HTTP's method vocabulary was designed to describe operations on resources, not purposeful action. When an agent intends to SUMMARIZE a document, BOOK a resource, and SCHEDULE a sequence, all three arrive as POST requests. The server receives identical verbs with meaningfully different intent buried in request bodies, invisible to any protocol-level handler. AGTP response: a vocabulary of agent-native methods that express intent at the protocol level.

Problem 3: No Protocol-Level Identity, Authority, or Attribution for Agents When an AI agent takes an action, there is currently no protocol-level mechanism to verify who authorized this agent, what scope of authority it holds, which principal is accountable for its actions, or whether it is the agent it claims to be. Accountability gaps, authority laundering, auditability failure, and multi-agent trust collapse result. AGTP response: agent identity and authority scope embedded in protocol headers on every request, with an optional Agent Certificate extension for cryptographic verification.

Problem Summary Summary of Problems Addressed by AGTP

#	Problem	Current Failure	AGTP Response
1	Undifferentiated traffic	HTTP cannot separate agent traffic	Dedicated protocol environment
2	Semantic mismatch	HTTP verbs obscure agent intent	Native intent-based method vocabulary
3	No protocol-level identity	Attribution is untraceable	Agent identity and scope in headers

Related Work and Existing Approaches

HTTP/REST as the De Facto Standard HTTP remains the universal transport for all agent traffic currently deployed. REST conventions layered on HTTP provide a degree of semantic structure, but REST remains a resource-manipulation paradigm. As described in Section 1.3, evolving HTTP to address agent-specific needs is constrained by the frozen method registry, backward-compatibility requirements, and the impossibility of achieving infrastructure-level traffic differentiation through HTTP extensions alone.

Existing Agent Group Messaging Protocols

MCP (Model Context Protocol, Anthropic):: Defines structured communication between AI models and tools/resources. Runs over HTTP. Addresses tool-calling semantics, not agent traffic transport.
ACP (Agent Communication Protocol, IBM):: Defines messaging semantics for agent-to-agent communication. Runs over HTTP.
A2A (Agent-to-Agent Protocol, Linux Foundation):: Defines inter-agent communication and task delegation semantics. Runs over HTTP.
ANP (Agent Network Protocol):: Defines discovery and communication for networked agents. Runs over HTTP.

All of these are messaging protocols. They define what agents say to each other. They do not define how agent traffic moves across a network. Each presupposes HTTP as its transport and inherits all of HTTP's limitations for agentic systems.

Transport-Layer Alternatives

gRPC:: High-performance RPC over HTTP/2. Strong typing and efficient serialization. Does not address agent-specific semantics, identity, or authority.
WebSockets:: Persistent bidirectional connections over HTTP. Useful for real-time communication but does not address method semantics or identity.
QUIC :: Modern multiplexed transport with reduced connection overhead. AGTP SHOULD prefer QUIC for new implementations. QUIC is a transport primitive; AGTP is the application-layer protocol above it.

The Critical Distinction: Messaging vs. Transport The most important positioning principle for AGTP is the distinction between messaging protocols and transport protocols. MCP, ACP, A2A, and ANP are messaging protocols, they define what agents say. AGTP defines how agent traffic moves. An analogy: SMTP is a messaging protocol that runs over TCP. SMTP does not replace TCP. Saying "TCP is unnecessary because SMTP exists" is a category error. The same logic applies here. MCP and its peers define agent messaging semantics. AGTP defines the transport environment those messages move through.

AGTP Positioning: The Proposed Stack

AGTP in the Protocol Stack AGTP is not a replacement for messaging protocols. Agents using MCP or A2A route those messages over AGTP and gain transport-level observability and identity without modifying the messaging layer. AGTP-native agents that do not use a separate messaging protocol interact with AGTP methods directly.

Protocol Overview

Stack Position AGTP is an application-layer protocol. It operates above the transport layer (TCP, UDP, or QUIC) and is wrapped by TLS. It sits below any agent messaging protocol in deployments that use one.

SHOULD prefer QUIC for new deployments (lower latency, multiplexing without head-of-line blocking, 0-RTT connection establishment).
MUST support TCP/TLS as a fallback for compatibility with existing infrastructure.
MAY run over UDP where QUIC is not available, subject to implementor-defined reliability guarantees.

Suggested port assignment (subject to IANA assignment. See Section 8):

AGTP/QUIC: port 8443 (proposed)
AGTP/TCP+TLS: port 8080 (proposed)

Design Principles

Minimalist core:: The base spec defines only what is necessary for agent traffic differentiation, method semantics, and identity headers. Extensions belong in companion specifications.
Extensible by design:: New methods are registered through an IANA-managed Method Registry. New header fields follow a defined extension convention. Additive changes do not require a version increment.
Agent-native:: Every design decision assumes the initiating party is an AI system, not a human.
Secure by default:: TLS 1.3 or higher is mandatory. Unencrypted AGTP connections MUST be rejected. Agent identity headers are present on every request.
Observable by design:: Native metadata in every AGTP header provides the minimum information needed for routing, monitoring, and audit without application-layer instrumentation.
Composable:: AGTP works alongside existing agent messaging protocols without requiring modification to those protocols.

Connection Model AGTP uses a persistent session model by default, reflecting the reality that agents typically execute multi-step workflows rather than isolated single requests. An AGTP session is established with a single TLS handshake including agent identity assertion, persists across multiple method exchanges, carries a Session-ID header identifying the agent's task context, and terminates on explicit session close or inactivity timeout (RECOMMENDED minimum: 60 seconds). Per-request (stateless) mode is supported for constrained environments. In stateless mode, agent identity headers MUST be present on every individual request.

Header Format

Request Headers AGTP Request Header Fields

Field	Required	Description
AGTP-Version	MUST	Protocol version. Current: AGTP/1.0
AGTP-Method	MUST	The agent intent method (see Section 6)
Agent-ID	MUST	Opaque identifier for the requesting agent instance
Principal-ID	MUST	Identifier of the human or system that authorized this agent
Authority-Scope	MUST	Declared scope of actions this agent is authorized to take
Session-ID	SHOULD	Identifies the current task/workflow context
Task-ID	SHOULD	Unique identifier for this specific method invocation
Delegation-Chain	MAY	Ordered list of Agent-IDs if this request was delegated
Priority	MAY	Request priority hint: critical, normal, background
TTL	MAY	Maximum acceptable response latency in milliseconds
Budget-Limit	MAY	Max resource budget per invocation. Format: space-separated `unit=value` tokens. Units from IANA AGTP Budget Unit Registry.
AGTP-Zone-ID	MAY	Network zone boundary constraint. SEPs MUST enforce; return 453 if DELEGATE or COLLABORATE would exit declared zone.
Content-Schema	MAY	URI reference to JSON Schema describing the request body structure. Enables receivers to validate payload without LLM inference.
Telemetry-Export	MAY	OTLP endpoint URI for metric export, or `inline` to receive metrics embedded in the response Attribution-Record.
Merchant-ID	MUST on PURCHASE	Canonical identifier of the intended merchant counterparty. See .
Merchant-Manifest-Fingerprint	MUST on PURCHASE	SHA-256 fingerprint of the Merchant Manifest Document verified by the requesting agent. Receiving server MUST reject with 455 if this does not match its current manifest. See .
Intent-Assertion	SHOULD on PURCHASE	Detached JWT carrying signed principal-authorized purchase intent. Forwardable to payment networks as standalone evidence. See .
Cart-Digest	MAY	Cryptographic digest of a structured cart returned by a prior QUOTE invocation. Binds a PURCHASE to a previously quoted cart without retransmission of line-item detail. See .

Response Headers AGTP Response Header Fields

Field	Required	Description
AGTP-Version	MUST	Protocol version
AGTP-Status	MUST	Numeric status code (see Section 5.5)
Task-ID	MUST	Echo of request Task-ID for correlation
Server-Agent-ID	SHOULD	Identity of the responding server or agent
Attribution-Record	SHOULD	Signed record of the action taken, for audit. MAY include RATS attestation evidence and inline telemetry when Telemetry-Export is set to `inline`.
Continuation-Token	MAY	Token for retrieving additional results in streaming contexts
Supported-Methods	SHOULD (on session open)	List of AGTP methods supported by this server
Cost-Estimate	MAY	Estimated resource consumption in Budget-Limit unit format. Returned by QUOTE; MAY appear on any response as an informational signal.
Attestation-Evidence	MAY	RATS attestation evidence token or reference URI per . Format indicated by `attestation_type` in response body: `rats-eat`, `rats-corim`, or `rats-uri`.

Status Codes AGTP defines its own status code space. Codes 451, 452, 453, 550, and 551 are AGTP-specific with no HTTP equivalent and are registered in the IANA AGTP Status Code Registry (see Section 9.3). AGTP Status Codes

Code	Name	Meaning
200	OK	Method executed successfully
202	Accepted	Method accepted; execution is asynchronous
204	No Content	Method executed; no response body
400	Bad Request	Malformed AGTP request
401	Unauthorized	Agent-ID not recognized or not authenticated
403	Forbidden	Agent lacks authority for requested action per Authority-Scope
404	Not Found	Target resource or agent not found
408	Timeout	TTL exceeded before method could execute
409	Conflict	Method conflicts with current state (e.g., BOOK on unavailable resource)
410	Gone	Agent has been Revoked or Deprecated; canonical ID is permanently retired
422	Unprocessable	Request well-formed but semantically invalid
429	Rate Limited	Agent is exceeding permitted request frequency
451	Scope Violation	Requested action is outside declared Authority-Scope. AGTP-specific
452	Budget Exceeded	Method execution would exceed the Budget-Limit declared in the request. AGTP-specific
453	Zone Violation	Request would route outside the AGTP-Zone-ID boundary. SEP-enforced. AGTP-specific
455	Counterparty Unverified	PURCHASE counterparty failed merchant identity verification: Merchant-ID absent, Merchant-Manifest-Fingerprint mismatch, or merchant in non-Active lifecycle state. AGTP-specific. See .
500	Server Error	Internal failure in the responding system
503	Unavailable	Responding agent or system temporarily unavailable or Suspended
550	Delegation Failure	A delegated sub-agent failed to complete the requested action. AGTP-specific
551	Authority Chain Broken	Delegation chain contains an unverifiable or broken identity link. AGTP-specific

Status code 451 (Scope Violation) is a governance signal: the agent attempted an action outside its declared Authority-Scope, caught at the protocol level. Status code 452 (Budget Exceeded) is a governance signal analogous to 451: the agent's requested action is within its Authority-Scope but would consume resources beyond what the principal authorized for this invocation. Status code 453 (Zone Violation) is returned by SEPs when a DELEGATE or COLLABORATE request would route to an agent outside the declared AGTP-Zone-ID boundary. Status code 455 (Counterparty Unverified) is returned on PURCHASE invocations when the receiving server cannot verify that the requesting agent has performed valid merchant identity verification against the server's current Merchant Manifest Document, or when the merchant is in a non-Active lifecycle state; see . Status code 551 (Authority Chain Broken) indicates that one or more Agent-ID entries in the Delegation-Chain header cannot be verified as part of a valid delegation sequence. Status code 410 (Gone) is returned when an agent's Birth Certificate has been revoked or the agent deprecated; the canonical Agent-ID is permanently retired and MUST NOT be retried. All AGTP-specific status codes are operational signals, not protocol errors, and MUST be logged for audit purposes.

Wire Format and Content-Type AGTP request and response bodies are encoded as JSON. The registered Content-Type for AGTP message bodies is: Implementations MUST include this Content-Type on all AGTP requests and responses that carry a message body. Responses with no body (e.g., 204 No Content) MUST NOT include a Content-Type header. Binary or streaming extensions MAY define additional Content-Type values as part of their companion specifications. The common structure for all AGTP request bodies: And for all AGTP response bodies:

Early Implementations AGTP is a proposed specification. No production implementations exist at the time of this writing. The author encourages early prototype implementations to validate the protocol design, identify gaps, and generate feedback prior to IETF working group submission.

If you are building an AGTP prototype or reference implementation, please share your findings via the feedback channel listed on the cover of this document. A reference implementation in Python and/or Go is planned as open-source software concurrent with or shortly after IETF I-D submission. Implementation reports are welcome and will be incorporated into subsequent draft revisions.

Implementers wishing to experiment before the formal IANA port assignment may use port 8443 (AGTP/QUIC) and port 8080 (AGTP/TCP+TLS) as working values. These values are subject to change upon final IANA assignment. The ACTIVATE method extension, which binds .nomo governed agent packages to AGTP as a first-class activation operation, is described in a companion document and is implemented as an optional extension. Core AGTP implementations need not support ACTIVATE to be compliant with this specification.

Agent Identity, URI Structure, and Registration

URI Structure and Resolution Mechanics

Foundational Principle AGTP identity is agent-first. Every agent is identified by a canonical Agent-ID: a 256-bit cryptographic identifier derived from the agent's Birth Certificate hash at ACTIVATE time. The canonical Agent-ID is the authoritative identifier in every AGTP protocol operation. It appears in the Agent-ID header of every request, is the key in the registry, and is the cross-layer reference linking the AGTP Agent Certificate extension to the governance-layer Birth Certificate. All other identification forms recognized by AGTP, including domain- anchored URIs, agent-native hierarchical names, and Web3 resolution targets, are aliases that resolve to a canonical Agent-ID. In the event of any conflict between an alias and a canonical Agent-ID, the canonical Agent-ID MUST be treated as authoritative. AGTP URIs are addresses, not filenames. File format suffixes (.agtp) MUST NOT appear in canonical agtp:// URIs. A URI resolves to an Agent Manifest Document or Agent Namespace Document derived from the underlying package; it does not expose or serve the package itself. Implementations MUST treat any URI containing a file extension in the path as non-canonical and SHOULD issue a 301 Moved Permanently redirect to the canonical form prior to resolution. The distinction between .agent and .nomo as agent-native hierarchical TLDs (Section 5.1) and their use as file format suffixes is resolved by position: agent-native TLDs appear in the hostname position of the URI; file format suffixes appear in the path position and are prohibited there.

Canonical URI Forms AGTP defines the following canonical URI forms. Form 1 is the authoritative identity form; Forms 2 through 5 are resolution aliases that MUST resolve to the same canonical Agent-ID as Form 1. Form 1 resolves to a signed Agent Manifest Document through any verification path declared in the agent's registry record (Section 5.2). The canonical ID is self-describing: any AGTP-aware governance platform, transparency log, or resolution service can return the Manifest Document given the canonical ID alone, without prior knowledge of which organization, domain, or blockchain the agent is registered under. Form 2 uses the agent-native hierarchical namespace governed by the AGTP resolution layer rather than by DNS. The .agent TLD is reserved within the AGTP namespace for general-purpose agents; the .nomo TLD is reserved for agents activated under the governed .nomo package format. Resolution of Form 2 URIs follows the disambiguation rules defined below when the same label is also present in a Web3 naming system. Form 3 and Form 4 use DNS to resolve an org domain to a governance platform endpoint. These forms are convenient where the organization already holds a verified DNS presence and prefers DNS-anchored discovery. They are equivalent to Form 2 for identity purposes; the difference is the resolution path, not the identity model. The following URI forms remain invalid and MUST return 400 Bad Request with error code invalid-uri-form: These prohibitions apply to file format suffixes in the path position only. The .agent and .nomo labels remain valid in the hostname position as agent-native TLDs (Form 2 and Form 5).

Namespace Disambiguation with Web3 Resolution The .agent label is also claimed as a top-level domain by at least one blockchain-based naming system. To prevent ambiguous resolution, AGTP implementations MUST apply the following rules when resolving a URI whose hostname ends in .agent or .nomo:

Query the AGTP governance platform registry first. If the URI resolves to a registered agent in Active lifecycle state, return the Agent Manifest Document. This is the AGTP-native path and is authoritative.
If the AGTP registry returns no match, and if the implementation supports Web3 resolution per , query the Web3 naming system. If the Web3 resolution returns an AGTP-compatible record, return the Agent Manifest Document derived from that record.
If neither path returns a match, return 404 Not Found.

Canonical Agent-ID (Form 1) remains authoritative in all cases. An agent registered through both AGTP-native and Web3 paths MUST produce the same canonical Agent-ID through either resolution path. Conflict between paths MUST be resolved in favor of the canonical Agent-ID recorded in the governance platform's Birth Certificate.

Non-Canonical Forms and Redirect Behavior The following non-canonical forms SHOULD be redirected to their canonical equivalents. Implementations MUST NOT serve package contents in response to any URI form. Non-Canonical URI Forms and Redirect Targets

Received URI	Canonical Redirect Target
`agtp://acme.tld/agents/customer-service.agent`	`agtp://acme.tld/agents/customer-service`
`agtp://acme.tld/agents/customer-service.nomo`	`agtp://acme.tld/agents/customer-service`
`agtp://acme.tld/agents/customer-service.agtp`	`agtp://acme.tld/agents/customer-service`

Query Parameters for Format Selection All AGTP URI resolution requests accept an optional format query parameter controlling the serialization of the returned document. AGTP URI Format Query Parameters

Query Parameter	Returned Representation
(none)	Agent Manifest Document, human-readable `application/agtp+json`
`?format=manifest`	Agent Manifest Document, human-readable `application/agtp+json`
`?format=json`	Agent Manifest Document, compact `application/agtp+json`
`?format=certificate`	Birth certificate fields only, `application/agtp+json`
`?format=status`	Lifecycle state and operational status only, `application/agtp+json`

All format variants return signed application/agtp+json content. The ?format=json parameter is intended for programmatic consumers. The default returns the full human-readable manifest suitable for browser rendering by an AGTP-aware client.

Resolution Mechanics AGTP URI resolution proceeds according to the URI form presented. Form 1 (canonical ID) resolves through a registry or log lookup; Forms 2 through 5 resolve through a hierarchical name lookup. All forms terminate in a signed Agent Manifest Document derived from the same Birth Certificate.

Form 1 Resolution (Canonical ID) When an AGTP resolver receives a URI of the form agtp://[256-bit-hex-id], it MUST perform the following steps:

Parse and validate the canonical Agent-ID. If the identifier is malformed (length, character set), return 400 Bad Request with error code invalid-canonical-id.
Query the agent's governance platform registry for the record associated with the canonical Agent-ID. If the resolver does not know which governance platform holds the record, it MAY query a transparency log per Section 5.2 to locate the record.
Verify the registry record lifecycle state. If Suspended, return 503 Service Unavailable with lifecycle state in the response body. If Revoked or Deprecated, return 410 Gone with lifecycle state and revocation timestamp.
Retrieve the agent's package (.agent or .nomo) from the package store referenced by the registry record.
Verify the package integrity hash before proceeding. If integrity verification fails, return 500 Internal Error with error code package-integrity-failure. MUST be logged.
Extract the embedded manifest from the verified package.
Sign the manifest document using the governance platform's signing key. Return the signed application/agtp+json document in the format specified by the query parameter.

Form 1 resolution does not require prior knowledge of an organization domain, a DNS record, or a Web3 naming anchor. The canonical Agent-ID is sufficient input.

Forms 2-5 Resolution (Hierarchical and Domain-Anchored) When an AGTP resolver receives a URI of Form 2, 3, 4, or 5, it MUST perform the following steps:

Parse and validate the URI. If the URI is an invalid (prohibited) form, return 400 Bad Request with error code invalid-uri-form.
For Form 2 and Form 5 URIs whose hostname ends in .agent or .nomo, apply the namespace disambiguation rules in Section 5.1.
Resolve the hierarchical name or domain+label pair to a canonical Agent-ID via the governance platform's registry lookup. If no matching agent is found, return 404 Not Found.
Continue with Form 1 resolution steps 3 through 7 using the resolved canonical Agent-ID.

The package's executable content, code, logic, and any fields not included in the manifest schema MUST NOT be returned at any step of any resolution path. URI resolution exposes identity and status exclusively.

Verification Paths and Trust Tier Assignment AGTP recognizes multiple equivalent verification paths for Trust Tier 1. Each path produces the same identity primitive: a canonical Agent-ID derived from a governance-platform-signed Birth Certificate. The verification path in use MUST be declared in the verification_path field of the Birth Certificate and is surfaced in the Agent Manifest Document.

Trust Tier 1 - Verified:

Tier 1 agents are eligible for the full Authority-Scope vocabulary, delegation chains, financial transactions, and multi-organization collaboration. Tier 1 verification requires exactly one of the following paths to succeed at ACTIVATE time. The verification path chosen does not affect the identity model or the canonical Agent-ID; it affects only the evidence chain backing the Birth Certificate. Trust Tier 1 Verification Paths

Path	Mechanism	Evidence Anchor
`dns-anchored`	RFC 8555 ACME challenge against claimed `org_domain`	DNS TXT record
`log-anchored`	Birth Certificate inclusion in AGTP transparency log	Log inclusion proof (RFC 9162 VDS, RFC 9943 receipt)
`hybrid`	DNS challenge combined with blockchain address signature	DNS TXT record + blockchain signature

dns-anchored: The governance platform MUST verify that the registering party controls the DNS zone for the claimed org_domain before issuing a Tier 1 Birth Certificate. Dns-anchored agents MUST have the following DNS record published and verifiable at resolution time: log-anchored: The governance platform MUST submit the Birth Certificate to an AGTP-aligned transparency log and record the resulting inclusion proof in the registry record. The log MUST implement the verifiable data structure defined in and SHOULD issue COSE_Sign1 receipts per (SCITT) for cross-ecosystem interoperability. A log-anchored agent is verifiable by any party with access to the transparency log, without dependence on DNS ownership. The log server protocol, receipt schema, and federation model are specified in . hybrid: The governance platform MUST verify both DNS control over the claimed domain and ownership of the declared blockchain address via signature challenge. This path is used by agents whose identity is anchored in a Web3 naming system and who also hold a verified DNS presence. See . All Tier 1 paths require a .nomo governed package.

Trust Tier 2 - Org-Asserted:

For agents operating within a single organization's internal infrastructure, or where no Tier 1 verification path has been completed. The registering party asserts an organizational affiliation without cryptographic proof. The Agent Manifest Document for Tier 2 agents MUST include a trust_tier: 2 field and a trust_warning field with value "verification-incomplete". AGTP-aware browsers and clients MUST surface a visible trust indicator distinguishing Tier 2 from Tier 1. Tier 2 agents MUST NOT be granted authority scopes above documents:query and knowledge:query without the AGTP Agent Certificate extension providing cryptographic identity binding at the transport layer.

Trust Tier 3 - Experimental:

Agent label uses the X- prefix. Not discoverable through the public AGTP registry. For development and testing only. Implementations MUST NOT deploy Tier 3 agents in production.

Subdomain Deployment Pattern Organizations SHOULD deploy AGTP endpoints at a dedicated subdomain following the pattern agtp.[organization-domain.tld] (e.g., agtp.acme.tld). This is the recommended enterprise deployment pattern: it provides clean separation between web and agent infrastructure, allows independent certificate management for the AGTP endpoint, and is consistent with service-specific subdomain conventions. An organization with an AGTP subdomain SHOULD also configure their primary domain to redirect AGTP requests:

The /agents/ Reserved Path Prefix The path prefix /agents/ is reserved in all agtp:// URIs for agent namespace operations. Implementations MUST support this prefix. The registry root at /agents (no trailing label) resolves to the Agent Namespace Document (see Section 5.4).

Collision Prevention The canonical Agent-ID is the collision-prevention primitive. Two canonical Agent-IDs are distinct if and only if the 256-bit identifiers differ, and the governance platform enforces uniqueness at issuance time by deriving the ID from the Birth Certificate hash. For alias forms, collision prevention operates at the namespace level. agtp://acme.tld/agents/customer-service and agtp://chrishood.tld/agents/customer-service resolve to distinct canonical Agent-IDs because they are registered under different org_domain values. Similarly, agtp://customer-service.acme.agent and agtp://customer-service.chrishood.agent resolve to distinct canonical Agent-IDs because they are registered under different agent-native org labels. Within a single governance zone, the governance platform enforces uniqueness of agent labels at registration time. Infrastructure MUST use the canonical Agent-ID for all routing, logging, and attribution operations. Alias URIs are a display and discovery layer only. An alias that resolves to a canonical Agent-ID different from the one carried in the Agent-ID header on a request MUST cause the request to be rejected with 401 Unauthorized and MUST be logged.

IANA Considerations for the agtp:// URI Scheme This document proposes registration of the agtp:// URI scheme with IANA per . Registration template:

URI scheme name:: agtp
Status:: Permanent
URI scheme syntax:: agtp://[canonical-agent-id] (authoritative) agtp://[label].[org-label].agent or agtp://[label].[org-label].nomo (agent-native hierarchical) agtp://[domain.tld]/agents/[label] (domain-anchored) agtp://agtp.[domain.tld]/agents/[label] (subdomain-anchored) agtp://[org-label].agent or agtp://[domain.tld]/agents (namespace root)
URI scheme semantics:: Identifies an AI agent or agent namespace operating over the Agent Transfer Protocol. The authoritative form uses a 256-bit hex-encoded cryptographic identifier derived from the agent's Birth Certificate. The agent-native hierarchical form uses AGTP-governed .agent or .nomo top-level labels. The domain-anchored form uses a verified or asserted organization DNS domain with a reserved /agents/ path prefix. All alias forms MUST resolve to the same canonical Agent-ID.
Applications/protocols that use this URI scheme:: Agent Transfer Protocol (this document)
Interoperability considerations:: The canonical Agent-ID form is the authoritative identity representation. Agent-native hierarchical URIs are governance- platform-resolved and require the disambiguation rules in Section 5.1 when coexisting with Web3 naming systems. Domain-anchored URIs resolve through DNS to a governance platform endpoint. Implementations MUST accept canonical Agent-IDs and SHOULD support at least one alias form. File format suffixes (.agtp) MUST NOT appear in agtp:// URIs.
Contact:: Chris Hood, chris@nomotic.ai
References:: This document

The agtp:// URI scheme registration is open and unencumbered. No intellectual property claims apply to the URI scheme itself.

Trust Tier Summary AGTP Trust Tier Summary

Trust Tier	Verification Paths (any one sufficient)	Package Required	Registry Visible
1 - Verified	DNS challenge per ; OR log inclusion per / ; OR hybrid DNS + blockchain signature	`.nomo`	Yes
2 - Org-Asserted	None (affiliation asserted without proof)	`.agent` or `.nomo`	Yes (with warning)
3 - Experimental	None	Any	No

The verification path used for a Tier 1 agent is recorded in the verification_path field of the Birth Certificate (dns-anchored, log-anchored, or hybrid) and surfaced in the Agent Manifest Document. All Tier 1 paths produce identity attestations of equivalent strength for AGTP protocol purposes.

Agent Namespace Document

Purpose and Scope The Agent Namespace Document is the index of all Active agents registered under an organization's governance zone. It is returned in response to a request targeting the /agents path: The Agent Namespace Document is not a manually editable file. It is generated and cryptographically signed by the governance platform each time the registry changes. Any Namespace Document that fails signature verification MUST be rejected by the requesting party.

Document Schema

Agent Namespace Document Schema The agents array MUST include only agents in Active lifecycle state. Suspended, Revoked, and Deprecated agents MUST NOT appear in the Namespace Document.

Integrity and Freshness The Namespace Document MUST include a generated_at timestamp. Implementations SHOULD treat Namespace Documents older than a configurable freshness threshold (default: 300 seconds) as stale and re-request. The governance platform MUST re-sign the Namespace Document within 60 seconds of any registry change. The signature covers the entire document including generated_at. Replaying an older signed Namespace Document to conceal a revocation event is a known attack vector; implementations MUST reject Namespace Documents with a generated_at timestamp older than the freshness threshold.

Agent Manifest Document and the .agtp Format

Purpose and Scope The Agent Manifest Document is the protocol's canonical representation of a specific agent's identity, status, and behavioral scope. It is returned in response to any AGTP URI resolution request targeting a specific agent: The manifest is derived from the embedded manifest inside the agent's .agent or .nomo package. It is not a separate file that can be independently modified. The governance platform MUST verify the package integrity hash before extracting and serving the manifest.

The Three Document Formats and Their Relationship

Relationship Between AGTP File Formats The .agtp format is the protocol's own document type. It is what gets transmitted over the wire. The .agent and .nomo formats are what get deployed. An AGTP implementation is not required to understand .agent or .nomo packaging internals; it is only required to produce and consume .agtp manifest documents. Additional packaging formats MAY be defined by third parties, provided they can produce conformant .agtp manifest documents when queried. Such formats MUST implement the integrity verification requirement: the manifest MUST be derived from a verified package, not from an independently stored or editable file.

Agent Manifest Document Schema The following fields are REQUIRED in all Agent Manifest Documents:

Agent Manifest Document - Required Fields The following fields are RECOMMENDED:

Agent Manifest Document - Recommended Fields The verification_path field surfaces the Tier 1 verification path used at ACTIVATE time. Its value MUST match the verification_path field of the underlying Birth Certificate. The dns_anchor_record field is populated when verification_path is dns-anchored or hybrid. The log_inclusion_proof field is populated when verification_path is log-anchored and carries the transparency log inclusion proof per or the COSE_Sign1 receipt per . The following fields are REQUIRED when trust_tier is 2:

Agent Manifest Document - Required Fields for Trust Tier 2

What the Manifest Exposes and Does Not Expose The Agent Manifest Document MUST expose:

The agent's identity (canonical ID, label, org, governance zone)
The agent's current operational status (lifecycle state)
The agent's authority scope categories
The agent's supported method vocabulary
The agent's behavioral trust score
The agent's birth certificate fields (activated_at, principal_org)
The agent's trust tier and any associated trust warnings

The Agent Manifest Document MUST NOT expose:

Executable code, scripts, or logic
Model weights or configurations
Internal API keys or credentials
Specific authority scope grant tokens
Session history or prior action logs

No AGTP URI resolution path, including any query parameter combination, MUST return package contents beyond the manifest schema defined in this section.

Manifest Tamper-Proofing The tamper-proof guarantee rests on two mechanisms:

Package integrity hash: Any modification to the package or its embedded manifest invalidates the hash. The governance platform MUST verify this hash before extracting the manifest.
Document signature: The governance platform signs the extracted manifest before serving it. The signature covers the full document including the package_integrity_hash field, creating a verifiable chain from the served document back to the registered package.

A manifest document that fails either verification step MUST be rejected, MUST NOT be served, and the failure MUST be logged.

Browser and Human-Facing Interaction Model

The Separation of Discovery and Execution

AGTP URI Use by Audience The analogy to existing protocol conventions is direct. A mailto: URI surfaces an address and hands off to a mail client; SMTP carries the actual messages. Similarly, an agtp:// URI surfaces identity and status; AGTP carries agent traffic. Browsers do not become AGTP clients by following an agtp:// link.

Browser Behavior for agtp:// URIs Browsers that encounter an agtp:// URI SHOULD behave as follows:

If a registered AGTP client is present (OS protocol handler), hand off the URI to that client.
If the browser supports agtp:// natively or via extension, render the returned Agent Manifest Document as a structured human-readable page. The rendered view MUST surface the trust tier indicator prominently, following the visual convention established for TLS trust in the browser chrome.
If neither condition applies, the browser MAY fall back to a gateway that translates between https:// and agtp://. The gateway MUST preserve all signature and trust tier fields.

Human-Readable Manifest View When an Agent Manifest Document is rendered for human consumption, the following fields MUST be prominently displayed:

Agent label and org domain
Trust tier indicator (visual distinction between Tier 1, 2, and 3)
Lifecycle state (Active / Suspended / Revoked / Deprecated)
Job description
Principal organization
Activation date
Behavioral trust score
Authority scope categories (in human-readable form)

AGTP Status Sub-Resource Implementations SHOULD support a status sub-path:

AGTP Status Sub-Resource Response The active_session_count field SHOULD only be included if the requester has appropriate observability permissions for the governance zone.

Web3 Interaction Considerations

Namespace Coexistence with Web3 Naming Systems The .agent label is claimed as a top-level domain by at least one blockchain-based naming system. In v04 of this specification, the response to this collision was to prohibit .agent and .nomo from the hostname position of agtp:// URIs. Version 05 reverses that approach. The agent-native hierarchical namespace is restored, and coexistence with Web3 naming is handled through the deterministic resolution order specified in Section 5.1: AGTP-native registry lookup first, Web3 resolution second, with canonical Agent-ID as the authoritative tiebreaker.

Web3 as a Verification and Resolution Path AGTP identity is agent-first and anchored in the Birth Certificate. Verification paths (DNS, log, hybrid) and resolution paths (canonical ID, hierarchical name, domain lookup, Web3 lookup) are independent dimensions of the identity model. A Web3-anchored agent is not a second-class participant; it is an agent whose Birth Certificate was verified through the hybrid path and whose Agent Manifest Document is resolvable through a Web3 naming system in addition to the canonical ID. The verification_path field in the Birth Certificate replaces the v04 resolution_layer field and declares how the agent's identity was verified at ACTIVATE time: verification_path Field Values

Value	Meaning	Default Trust Tier
`dns-anchored`	DNS ownership verified via RFC 8555 ACME challenge	Tier 1
`log-anchored`	Birth Certificate inclusion in an AGTP transparency log per RFC 9162 / RFC 9943	Tier 1
`hybrid`	DNS ownership and blockchain address signature both verified	Tier 1
`org-asserted`	No cryptographic verification; affiliation asserted only	Tier 2

Implementations that encounter an agent whose Birth Certificate carries an unsupported verification_path value MUST treat the agent as Trust Tier 2 (trust_warning: "verification-path-unsupported") until an extension specification defining the value has been published and implemented. Full Web3 interoperability and hybrid verification procedures are specified in .

Agent Registration Process

Overview An agent cannot participate in AGTP until it has been issued an Agent Birth Certificate by a governance platform and assigned a canonical Agent-ID derived from that certificate. Canonical Agent-IDs are issued through the ACTIVATE transaction; they are never self-declared. The Birth Certificate is the genesis record of an agent's legal existence within the AGTP ecosystem. Its relationship to the canonical Agent-ID is analogous to the relationship between a government-issued birth registration and a social security number: the birth event produces a permanent, authoritative identity record, and a durable identifier is derived from it. The identifier follows the agent for its entire lifecycle, including after revocation. It is never reissued to another agent. Any AGTP infrastructure component MUST reject requests carrying an Agent-ID that does not resolve to a Birth Certificate record in an Active lifecycle state in a reachable registry.

Birth Certificate Contents The Agent Birth Certificate is issued by the governance platform at ACTIVATE time and contains the following fields: Agent Birth Certificate Fields

Field	Required	Description
`agent_id`	MUST	Unique identifier for the agent
`owner`	MUST	Human or team responsible for this agent
`archetype`	MUST	Behavioral category (see archetypes below)
`governance_zone`	MUST	Environment context (development, staging, production)
`scope`	MUST	Authorized action types
`issued_at`	MUST	Timestamp of issuance
`certificate_hash`	MUST	Cryptographic fingerprint - basis for canonical Agent-ID
`signature`	MUST	Signed with the org's governance key
`package_ref`	SHOULD	Reference to the `.agent` or `.nomo` package
`trust_tier`	MUST	Registration tier (1, 2, or 3)
`verification_path`	MUST (Tier 1)	Path used to verify identity: `dns-anchored`, `log-anchored`, `hybrid`, or `org-asserted`
`org_domain`	SHOULD	DNS-verified or asserted org domain (required for `dns-anchored` and `hybrid`)
`org_label`	SHOULD	Agent-native org label (required for Form 2 hierarchical resolution)
`log_inclusion_proof`	MUST (log-anchored)	Transparency log inclusion proof (RFC 9162 / RFC 9943)

Agent Archetypes The archetype field classifies the agent's behavioral category. Archetypes inform scope enforcement and observability tooling; an executor archetype agent exhibiting read-only query patterns, or a monitor archetype agent attempting booking operations, are anomaly signals. The archetype field does not restrict scope enforcement, Authority-Scope headers govern actual permissions at the protocol level. Archetypes are a classification and observability signal, not a security boundary. Agent Archetypes

Archetype	Description	Typical Scope
`assistant`	Conversational agent, read-heavy	`documents:query`, `knowledge:query`
`analyst`	Data analysis, read and aggregate	`data:read`, `data:aggregate`
`executor`	Takes real-world actions, write-heavy	`booking:*`, `payments:confirm`
`orchestrator`	Manages other agents	`delegation:`, `agents:`
`monitor`	Observational only	`telemetry:read`, `logs:read`

Birth Certificate to AGTP Header Mapping Birth Certificate fields map directly to AGTP protocol headers on every request. This mapping is the mechanism by which static identity (the Birth Certificate) becomes runtime identity (the protocol session): Birth Certificate to AGTP Header Mapping

Birth Certificate Field	AGTP Protocol Header
`agent_id`	`Agent-ID`
`owner`	`Principal-ID`
`scope`	`Authority-Scope`
`certificate_hash`	Basis for canonical Agent-ID

The canonical Agent-ID is derived from the certificate_hash. This chain, package integrity hash → certificate hash → canonical Agent-ID, ensures that the identifier carried in the Agent-ID header on every AGTP request is traceable back to the original Birth Certificate and the human principal who authorized the agent's creation.

Registration Tiers Tier 1 Registration (Verified): Required for agents carrying Authority-Scope beyond read-only query operations, or participating in delegation chains, financial transactions, or multi-agent collaboration with external organizations. Tier 1 registration requires exactly one of the three verification paths defined in Section 5.2 to succeed at ACTIVATE time. Common requirements for all Tier 1 paths:

Agent package MUST be in .nomo governed format
Package MUST include a valid CA-signed certificate chain
Governance platform MUST validate package integrity hash and certificate chain before issuing the Birth Certificate
Birth Certificate MUST record the specific verification_path used (dns-anchored, log-anchored, or hybrid)

Path-specific requirements:

dns-anchored: Registrant demonstrates DNS control over the claimed org_domain via DNS challenge per . Tier 1 _agtp TXT record MUST be published and verifiable at resolution time.
log-anchored: Governance platform submits the Birth Certificate to an AGTP-aligned transparency log implementing and records the inclusion proof in the registry. COSE_Sign1 receipts per (SCITT) SHOULD be issued for cross-ecosystem interoperability. The registering party is not required to control a DNS domain.
hybrid: Registrant demonstrates both DNS control and blockchain address ownership. Detailed procedure in .

Tier 2 Registration (Org-Asserted): For agents operating within a single organization's internal infrastructure, or where no Tier 1 verification path has been completed.

Requirements:

Organizational affiliation is declared but no cryptographic verification has been performed
Agent package may be .agent or .nomo format
Governance platform issues Birth Certificate after validating package integrity hash
Birth Certificate and Manifest MUST include trust_tier: 2 and trust_warning: "verification-incomplete"
Authority scope MUST be restricted at the SEP layer until upgraded to Tier 1

Tier 3 Registration (Experimental): For development and testing environments only.

Requirements:

Agent label MUST carry X- prefix
Not published to the public AGTP registry
MUST NOT be deployed in production environments
Governance platform issues a locally-scoped Birth Certificate

Registration Lifecycle

AGTP Agent Registration Lifecycle

Governance Tokens and Runtime Authorization Following successful registration, the agent's Birth Certificate is the static identity anchor. Runtime authorization for specific actions is carried by Governance Tokens: signed, time-limited JWT artifacts issued by the governance platform encoding a specific governance verdict (ALLOW, DENY) for a specific action. Governance Tokens MUST NOT be reused. Each action requires a fresh evaluation and a fresh token. Default TTL is 30 seconds. The token's agent_id field MUST match the canonical Agent-ID from the Birth Certificate. Tokens that fail this validation MUST be rejected and the failure MUST be logged. The relationship between Birth Certificate and Governance Token parallels the relationship between a passport and a visa: the passport establishes persistent identity; the visa encodes a specific time-bounded permission. Holding a passport does not imply holding any particular visa.

Friendly Name Availability and Re-Registration An agent label becomes available for re-registration 90 days after its associated agent enters Revoked or Deprecated lifecycle state. The canonical Agent-ID and Birth Certificate are permanently archived. The canonical Agent-ID MUST NOT be reissued under any circumstances, including re-registration of the same label by the same organization. This policy prevents ID reuse attacks in which a newly registered agent inherits the trust history of a revoked predecessor.

Method Definitions

Design Philosophy AGTP methods are intent verbs, not resource operations. Each method expresses what an agent is trying to accomplish. Method names are uppercase ASCII strings. Methods that modify state are NOT idempotent by default unless explicitly marked. All methods accept a context parameter carrying agent session state. Requirement language follows .

Core Methods

QUERY Purpose: Semantic data retrieval. The agent specifies what it needs to know, not where to find it. Distinguished from HTTP GET by expressing an information need rather than retrieving a known resource at a known location. QUERY Parameters

Parameter	Required	Description
intent	MUST	Natural language or structured expression of the information need
scope	SHOULD	Data domains or sources to include or exclude
format	MAY	Desired response format: structured, natural, raw
confidence_threshold	MAY	Minimum confidence score for included results (0.0-1.0)
context	MAY	Session context for disambiguation

Response: Result set with confidence scores per item. Server SHOULD indicate provenance of each result. Idempotent: Yes.

SUMMARIZE Purpose: Request a concise synthesis of provided content or a referenced resource. The agent is requesting a cognitive operation on data, not retrieving data. SUMMARIZE Parameters

Parameter	Required	Description
source	MUST	Content inline (up to implementation limit) or URI reference
length	SHOULD	Target summary length: brief, standard, detailed
focus	MAY	Aspect to emphasize in the summary
format	MAY	Output format: bullets, prose, structured
audience	MAY	Intended reader context, for calibrating complexity

Response: Summary content with a source_hash and a confidence score. Idempotent: Yes.

BOOK Purpose: Reserve a resource, time slot, seat, or allocation on behalf of the agent's principal. State-modifying. Notable error codes: 409 Conflict (resource unavailable), 451 Scope Violation (principal not authorized for this resource type). BOOK Parameters

Parameter	Required	Description
resource_id	MUST	Identifier of the resource to reserve
principal_id	MUST	The human or system on whose behalf the booking is made
time_slot	MUST (if time-based)	ISO 8601 datetime or range
quantity	MAY	Number of units to reserve
options	MAY	Resource-specific booking parameters
confirm_immediately	MAY	Boolean; if false, creates a hold pending confirmation

Response: Booking confirmation with booking_id, status (confirmed / held), and expiry timestamp if a hold. Idempotent: No.

SCHEDULE Purpose: Define a sequence of actions, method calls, or events to be executed at specified times or in response to specified triggers. Creates a durable plan, not an immediate execution. SCHEDULE Parameters

Parameter	Required	Description
steps	MUST	Ordered list of AGTP method calls with parameters
trigger	MUST	immediate, datetime, event, or condition
trigger_value	MUST (if not immediate)	Datetime, event name, or condition expression
on_failure	SHOULD	Behavior on step failure: abort, skip, retry, escalate
notify	MAY	Notification targets on completion or failure

Response: Schedule record with schedule_id, confirmed steps, and next execution timestamp. Idempotent: No.

LEARN Purpose: Update the agent's session context, knowledge state, or persistent memory. An explicit context write where the agent asserts that something should be retained. LEARN Parameters

Parameter	Required	Description
content	MUST	Information to be learned (structured or unstructured)
scope	MUST	session (ephemeral), principal (persists for principal), global (shared)
category	SHOULD	Semantic category for retrieval optimization
confidence	MAY	Agent's confidence in the content (0.0-1.0)
source	MAY	Provenance of the learned content
ttl	MAY	Expiry for the learned content

Response: Confirmation with learn_id and effective scope. Idempotent: No.

DELEGATE Purpose: Transfer execution of a task or method to a sub-agent or downstream system. Initiates a new AGTP session on behalf of the delegating agent, carrying forward authority lineage. DELEGATE Parameters

Parameter	Required	Description
target_agent_id	MUST	Identifier of the agent to delegate to
task	MUST	AGTP method call (or sequence) to execute
authority_scope	MUST	Scope granted to sub-agent MUST be a strict subset of delegating agent's scope
delegation_token	MUST	Signed token proving delegation authority
callback	SHOULD	AGTP endpoint for result delivery
deadline	MAY	Maximum time for task completion

Security note: the authority_scope in a DELEGATE request MUST NOT exceed the delegating agent's own Authority-Scope. Servers MUST enforce this and MUST return 451 Scope Violation if violated. This is the protocol-level defense against authority laundering. Idempotent: No.

COLLABORATE Purpose: Initiate a multi-agent coordinated task where two or more agents work in parallel or in defined roles toward a shared goal. Unlike DELEGATE (hierarchical), COLLABORATE is peer-to-peer. COLLABORATE Parameters

Parameter	Required	Description
collaborators	MUST	List of Agent-IDs invited to collaborate
objective	MUST	Shared goal expressed as a task description or structured specification
role_assignments	SHOULD	Map of Agent-IDs to roles within the collaboration
coordination_model	SHOULD	parallel, sequential, or consensus
result_aggregation	MAY	How results from collaborators are combined

Response: Collaboration session receipt with collaboration_id. Each collaborator receives an AGTP NOTIFY to join. Idempotent: No.

CONFIRM Purpose: Explicit acknowledgment of a prior action, state, or data item. Creates a signed attestation record. CONFIRM Parameters

Parameter	Required	Description
target_id	MUST	ID of the action, booking, schedule, or item being confirmed
status	MUST	accepted, rejected, or deferred
reason	SHOULD (if rejected/deferred)	Explanation of the decision
attestation	MAY	Agent-signed confirmation payload for audit

Response: Confirmation receipt with timestamp and attestation_id. Idempotent: Yes.

ESCALATE Purpose: Route a task, decision, or exception to a human principal or higher-authority agent when the current agent cannot or should not proceed. ESCALATE is the protocol-level expression of meaningful friction in AI systems as a first-class method. ESCALATE Parameters

Parameter	Required	Description
task_id	MUST	The task or method invocation triggering escalation
reason	MUST	Structured reason: confidence_threshold, scope_limit, ethical_flag, ambiguous_instruction, resource_unavailable
context	MUST	Full context needed for the escalation recipient to act
priority	SHOULD	urgent, normal, or low
recipient	MAY	Specific human or agent to escalate to; if absent, routes to default handler
deadline	MAY	Time by which a response is needed

Response: Escalation receipt with escalation_id and routing confirmation. The escalated task is paused until resolved via CONFIRM. Idempotent: Yes. An agent that escalates appropriately is functioning correctly. Governance frameworks built on AGTP can use escalation frequency and reason codes as observability signals for systemic issues.

NOTIFY Purpose: Asynchronous push of information from an agent to a recipient. Does not expect a response. Fire-and-forget. Delivery confirmation (if required) returned via a subsequent CONFIRM from the recipient. NOTIFY Parameters

Parameter	Required	Description
recipient	MUST	Target Agent-ID, human endpoint, or broadcast group
content	MUST	Notification payload
urgency	SHOULD	critical, informational, or background
delivery_guarantee	MAY	at_most_once, at_least_once, or exactly_once
expiry	MAY	Timestamp after which the notification should not be delivered

Response: Delivery receipt with notification_id. Idempotent: No.

DESCRIBE Purpose: Return the operational capabilities of a known agent endpoint. The requesting agent specifies what capability dimensions it needs to evaluate; the server returns a structured Capability Document. Used for pre-task negotiation before committing to DELEGATE or COLLABORATE. If capability_domains is omitted, the server SHOULD return all supported domains. Category: ACQUIRE. DESCRIBE Parameters

Parameter	Required	Description
capability_domains	SHOULD	Comma-separated domains to return: `methods`, `modalities`, `tools`, `version`, `budget`, `zones`. If omitted, server SHOULD return all.
version_min	MAY	Minimum acceptable version for capability negotiation.
context	MAY	Session context for capability filtering.

Response: Capability Document with the following structure: Idempotent: Yes. Primary error codes: 404, 422.

SUSPEND Purpose: Pause a specific active session workflow in a recoverable state. Issues a resumption nonce the requesting agent uses to resume the session. Method-level SUSPEND is session-scoped and does not affect registry lifecycle state or Birth Certificate validity. The distinction between method-level SUSPEND and lifecycle SUSPEND (Section 6.7.6) is architectural: method-level SUSPEND is a workflow primitive; lifecycle SUSPEND is an administrative action on the agent's registry record. Category: ORCHESTRATE. SUSPEND Parameters

Parameter	Required	Description
session_id	MUST	The session to suspend.
reason	SHOULD	Structured reason: `awaiting_input`, `resource_limit`, `scheduled_pause`, `external_dependency`.
resume_by	MAY	ISO 8601 deadline for resumption. If exceeded without RESUME, session transitions to expired.
checkpoint	MAY	Agent-provided state snapshot for resumption context. Stored by server for duration of suspension.

Response: Suspension receipt with the following structure: The resumption_nonce MUST be a cryptographically random 128-bit value encoded as base64url. It is single-use: once presented to resume a session, the nonce is invalidated and MUST NOT be accepted again. Idempotent: No. Primary error codes: 404, 408. Servers MUST generate nonces with at least 128 bits of entropy using a CSPRNG.

Method Summary Table AGTP Core Method Summary

Method	Intent	State-Modifying	Idempotent	Primary Error Codes
QUERY	Retrieve information	No	Yes	404, 422
SUMMARIZE	Synthesize content	No	Yes	400, 422
BOOK	Reserve a resource	Yes	No	409, 451
SCHEDULE	Plan future actions	Yes	No	400, 409
LEARN	Update agent context	Yes	No	400, 403
DELEGATE	Transfer task to sub-agent	Yes	No	403, 451, 551
COLLABORATE	Coordinate peer agents	Yes	No	404, 403
CONFIRM	Attest to a prior action	Yes	Yes	404, 400
ESCALATE	Defer to human/authority	Yes	Yes	404
NOTIFY	Push information	No	No	400, 404
DESCRIBE	Retrieve endpoint capabilities	No	Yes	404, 422
SUSPEND	Pause session workflow	Yes	No	404, 408
PROPOSE	Submit a dynamic endpoint proposal	Yes	No	400, 403, 460

Method Registry and Extensibility AGTP defines a formal Method Registry maintained by IANA (see Section 8.2). Any party may submit a new method for registration. The registration procedure is Expert Review, and registration MUST be accompanied by a published specification, at minimum an IETF Internet-Draft or equivalent publicly available document. Registered methods MUST:

Have a unique uppercase ASCII name
Define required and optional parameters
Define expected response structure
Specify idempotency behavior
Specify applicable error codes
Include a security considerations section
Be accompanied by a published reference specification (Internet-Draft or RFC)
Conform to the AGIS Grammar Specification , demonstrating membership in the action-intent semantic class as defined therein. Submissions that do not satisfy AGIS syntactic and semantic class requirements MUST be rejected by the Designated Expert.

Experimental methods MAY be used prior to registration using the X- prefix convention (e.g., X-NEGOTIATE). Experimental methods MUST NOT be used in production deployments without registration. Experimental methods MUST also conform to AGIS grammar rules; non-conformant experimental methods MUST NOT be forwarded by AGTP-aware infrastructure components.

Grammar-Based Method Validation (Method-Grammar Header) In addition to the IANA registry pathway, AGTP version 03 introduces a grammar-based method validation pathway. When an AGTP request carries the Method-Grammar header, the receiving infrastructure validates the method identifier against the declared grammar specification rather than checking the IANA registry exclusively. Behavior when Method-Grammar: AGIS/1.0 is present:

The AGTP infrastructure layer validates the method identifier against the AGIS Grammar Specification .
If the method identifier is AGIS-conformant (imperative base-form verb, action-intent semantic class, not an HTTP method or state descriptor), the request proceeds regardless of whether the method appears in the IANA registry.
If the method identifier fails AGIS validation, the infrastructure MUST return status 454 (Grammar Violation) and MUST NOT forward the request.
AGIS-conformant custom methods carry the same transport-level identity, authority scope, and governance semantics as registered methods.

This pathway enables organizations to define domain-specific Agentive API vocabularies -- RESERVE instead of BOOK, LOCATE instead of FIND, ADMIT and TRIAGE for healthcare contexts -- without requiring IANA registration while maintaining full AGTP transport governance. The IANA registry continues to serve as the reference vocabulary for maximum cross-system interoperability; the grammar pathway enables domain specificity within those constraints. Status code 454 Grammar Violation: Returned when a method identifier is present with Method-Grammar: AGIS/1.0 but fails AGIS grammar validation. The response body MUST include the specific validation failure from the AGIS eight-pass validator. This status code is registered in the AGTP Status Code Registry (see Section 8.3). Capability negotiation occurs during session establishment. The server returns a Supported-Methods header listing the methods it implements. Clients SHOULD check this list before invoking non-core methods. The Negotiation-ID header is used to correlate turns within a dynamic endpoint negotiation sequence (see Section 6.5). It MUST be a UUID generated by the service upon receiving a PROPOSE request and MUST be echoed in all subsequent turns of the same negotiation. Maximum three turns before the agent MUST ESCALATE. QUOTE is defined as a Tier 2 Standard Extended Method in . QUOTE provides pre-flight cost estimation for a proposed method invocation: the requesting agent submits a proposed method call; the server returns a Cost-Estimate response without executing the method. Servers supporting budget negotiation via the Budget-Limit header SHOULD implement QUOTE to enable agents to validate cost before committing to execution. Servers that implement QUOTE MUST list it in the Supported-Methods response header at session establishment.

Dynamic Endpoint Negotiation

Overview AGTP version 03 introduces a dynamic endpoint negotiation protocol enabling agents to discover data availability and instantiate endpoints on demand, without requiring pre-built API definitions. This protocol realizes the agentic API vision in which organizations expose data availability rather than pre-designed endpoints, and agents construct the interface they need at runtime. The negotiation protocol operates at the transport layer. AGIS provides the grammar for proposal and acceptance documents. The agent's identity and authority credentials (via the AGTP-CERT extension where deployed) govern authorization decisions.

Protocol Flow

PROPOSE Method PROPOSE is a Tier 1 AGTP method. The requesting agent submits an AGIS-formatted endpoint definition describing the interface it needs. The service evaluates whether it can fulfill the proposal against its data manifest and authorization policy. Parameters: PROPOSE Parameters

Parameter	Required	Description
proposal	Yes	Complete AGIS endpoint definition (method + path + semantic block + input schema + output schema)
session_id	Yes	The active AGTP session identifier
data_class	Yes	The data_manifest class the proposal targets
scope_requested	Recommended	The authority scope the agent requests for this endpoint
persistence	Optional	session (default) or persistent; persistent requires elevated authorization

Response on 263 Endpoint Instantiated: The proposed: true flag marks this as a dynamically instantiated endpoint per the AGIS specification .

Credential-Free Negotiation For data classes declared with sensitivity: informational and requires_authorization: false in the data manifest, services MAY complete the full negotiation flow without requiring credentials. The agent arrives, proposes, and receives an instantiated endpoint without API keys. For sensitive data classes, services MUST require credential establishment at Step 4a. The negotiation protocol is the mechanism by which credentials are established, not a prerequisite. This distinction is fundamental: the agent does not need credentials to begin a negotiation; it needs credentials to complete one for sensitive data. AGTP-CERT provides the cryptographic identity binding that enables services to make fine-grained authorization decisions during negotiation based on the agent's verified identity, principal, and authority scope.

Session Scope and Persistence Instantiated endpoints are session-scoped by default. They cease to exist when the AGTP session terminates. Services MAY offer persistent instantiation (the endpoint survives session termination and is added to the service's AGIS document) subject to elevated authorization. Persistent instantiation SHOULD be treated as a modification to the service's published AGIS document. Services supporting persistent instantiation MUST increment their AGIS-Version header on the next discovery request following persistence.

Extended Method Vocabulary and Industry Profiles

Three-Tier Method Architecture The AGTP method vocabulary is organized into three tiers reflecting different levels of universality, specificity, and domain relevance. All methods at all tiers MUST conform to the AGIS Grammar Specification . The AGIS action-intent semantic class constraint applies to every method in the IANA registry and to every AGIS-validated custom method accepted via the Method-Grammar header pathway.

Tier 1. Core Methods (defined in Section 6.2):: The baseline vocabulary required for AGTP compliance. Every conformant AGTP implementation MUST support all Tier 1 methods. All Tier 1 methods are AGIS-conformant; they are defined instances of the action-intent semantic class standardized in .
Tier 2. Standard Extended Methods:: Registered in the IANA AGTP Method Registry and available for use in any AGTP implementation. Not required for baseline compliance but SHOULD be implemented where their semantics apply. Defined in . All Tier 2 methods satisfy AGIS grammar requirements.
Tier 3. Industry Profile Methods:: Domain-specific method sets defined and registered by industry communities as named AGTP profiles. Valid within deployments that declare support for the relevant profile. Not required in general-purpose implementations. All Tier 3 profile method submissions MUST include AGIS conformance verification as part of their specification.
Tier 4. AGIS-Validated Custom Methods:: Organization-defined methods that are not registered in the IANA AGTP Method Registry but conform to the AGIS Grammar Specification and are accepted at the transport layer via the Method-Grammar: AGIS/1.0 header. Valid within the deploying organization's AGTP services. The action-intent semantic class constraint applies identically. Agents discover and interpret these methods through natural language inference against AGIS semantic declarations, as validated empirically in .

Method Category Taxonomy All AGTP methods are organized into five categories:

ACQUIRE:: Retrieve data, resources, or state without modifying it. Typically idempotent; no state modification.
COMPUTE:: Process, transform, or analyze information and produce a derived result. Typically idempotent given the same input.
TRANSACT:: Perform state-changing operations with external systems, resources, or records. Not idempotent by default; subject to reversibility classification.
COMMUNICATE:: Send information, notifications, or signals to recipients. Fire-and- forget or confirm-receipt delivery models.
ORCHESTRATE:: Coordinate, sequence, or manage multiple agents, tasks, or workflows. May spawn sub-agents or sessions; delegation chain semantics apply.

Core Method Category Mapping

Core Method	Category
QUERY	Acquire
SUMMARIZE	Compute
BOOK	Transact
SCHEDULE	Orchestrate
LEARN	Compute
DELEGATE	Orchestrate
COLLABORATE	Orchestrate
CONFIRM	Transact
ESCALATE	Orchestrate
NOTIFY	Communicate
DESCRIBE	Acquire
SUSPEND	Orchestrate
PROPOSE	Orchestrate

Standard Extended Methods (Tier 2) The following methods constitute the initial Tier 2 registration set, defined in . Listed here by category with brief semantic definitions; full parameter specifications are in the companion document. ACQUIRE category: FETCH, SEARCH, SCAN, PULL, IMPORT, FIND. COMPUTE category: EXTRACT, FILTER, VALIDATE, TRANSFORM, TRANSLATE, NORMALIZE, PREDICT, RANK, MAP. TRANSACT category: REGISTER, SUBMIT, TRANSFER, PURCHASE, SIGN, MERGE, LINK, LOG, SYNC, PUBLISH. COMMUNICATE category: REPLY, SEND, REPORT. ORCHESTRATE category: MONITOR, ROUTE, RETRY, PAUSE, RESUME, RUN, CHECK. Notable constraints: PURCHASE MUST carry explicit principal_id and scope enforcement; 451 Scope Violation applies if payments:purchase is not in the agent's Authority-Scope. RUN requires explicit procedure_id parameter; implementations MUST NOT accept free-form execution strings.

Short-Form and Industry-Inspired Methods A set of short-form verb methods, e.g., SET, TAKE, OPEN, START, CALL, MAKE, TURN, BREAK, are provisionally catalogued as candidates for Tier 2 registration. These verbs are highly context-dependent and their semantics vary significantly across deployment domains. Short-form methods will be registered individually only when a published companion specification provides unambiguous semantic definitions demonstrably distinct from existing registered methods. Provisional registrations using the X- prefix (e.g., X-SET, X-CALL) are encouraged during the experimentation period.

Industry Profile Method Sets AGTP recognizes that specific industries require method vocabularies reflecting domain-specific operations that would be inappropriate in a general-purpose standard. Industry profile method sets are defined and registered as named AGTP profiles. A profile is a published companion specification that:

Declares a profile name (e.g., agtp-profile-healthcare, agtp-profile-financial, agtp-profile-legaltech)
Defines one or more industry-specific methods with full parameter specifications, error codes, and security considerations
Specifies which Tier 1 and Tier 2 methods are REQUIRED, RECOMMENDED, or NOT APPLICABLE within the profile
Addresses regulatory or compliance considerations specific to the domain (e.g., HIPAA for healthcare, PCI-DSS for financial services)

Illustrative examples of potential industry profile methods (not yet registered; listed for directional purposes only): Healthcare: PRESCRIBE, AUTHORIZE, REFER, DISPENSE, TRIAGE, CONSENT, REDACT Financial services: SETTLE, RECONCILE, HEDGE, CLEAR, UNDERWRITE, KYC, AML Legal and compliance: ATTEST, NOTARIZE, DISCLOSE, REDLINE, EXECUTE, PRESERVE Infrastructure: PROVISION, DEPROVISION, ROLLBACK, SNAPSHOT, FAILOVER Industry communities are encouraged to develop and submit profile specifications through the IETF process. The IANA AGTP Method Registry will maintain a profile index alongside the core and standard method registries.

Registration Path for New Methods

For Tier 2 Standard Methods:: Submit an Internet-Draft to the IETF providing full method specification per Section 6.4. The Designated Expert reviews for semantic uniqueness, clarity, AGIS grammar conformance , and security considerations. Submissions that fail AGIS validation MUST be returned to the submitter before review proceeds.
For Industry Profile Methods (Tier 3):: Submit a profile specification to the IETF (or a recognized domain standards body with an established AGTP registry liaison) covering all methods in the profile and profile compliance requirements. The specification MUST include AGIS conformance statements for every method defined in the profile.
For AGIS-Validated Custom Methods (Tier 4):: No IANA registration required. The implementing organization defines its method vocabulary in an AGIS document served at the service's AGTP address. Methods are validated at the transport layer using the Method-Grammar: AGIS/1.0 header. The method vocabulary is declared in the AGIS vocabulary block and discoverable by agents at runtime. Organizations adopting Tier 4 methods are encouraged to publish their AGIS documents at agtp://[service-address] to enable cross-system agent discovery.
For Experimental Methods:: Use the X- prefix without registration. Implementations MUST NOT deploy experimental methods in production without completing either the IANA registration process (Tier 2/3) or deploying a conformant AGIS document (Tier 4). Experimental method names do not reserve the unprefixed name.

The AGTP Method Registry is published at: https://www.iana.org/assignments/agtp-methods/ The AGIS conformance test suite is maintained at: https://agtp.io/agis/conformance

Real-time Service Adaptation Services that update their AGIS documents at runtime MUST signal changes via the AGIS-Version response header. This header MUST be present on all AGTP responses from negotiable services. Agent runtimes MUST cache the AGIS-Version value from each service. When a response carries an AGIS-Version value different from the cached value, the agent runtime MUST re-fetch and re-validate the AGIS document before issuing further method calls. This mechanism supports real-time service adaptation without requiring push notifications. Services SHOULD increment AGIS-Version when: - A new endpoint is added to the AGIS document - An existing endpoint's semantic declaration changes - A new verb is added to the vocabulary block - A new data class is added to the data_manifest Services MUST NOT decrement or reuse AGIS-Version values.

Merchant Identity and Agentic Commerce Binding

Overview AGTP specifies agent-side identity through the Agent Birth Certificate, canonical Agent-ID, Agent Manifest Document, and Trust Tier model defined in Section 5. PURCHASE invocations carrying payments:purchase in the Authority-Scope header and a Budget-Limit constraint are fully governed on the sending side. The receiving side of a PURCHASE -- the merchant counterparty -- does not have an equivalent protocol-level identity in the base specification. Version 04 of AGTP introduces normative integration hooks for the AGTP Merchant Identity and Agentic Commerce Binding specification , which defines the merchant-side identity model. The integration is hook-based: this document registers the required headers, status code, and Authority-Scope domains; the detailed semantics, Merchant Manifest Document schema, Merchant Birth Certificate structure, and counterparty verification procedure are specified in the companion.

Merchant Identity Headers (Summary) PURCHASE invocations in a fully conformant v04 deployment carry the following additional headers:

Merchant-ID: canonical identifier of the intended merchant counterparty.
Merchant-Manifest-Fingerprint: SHA-256 fingerprint of the Merchant Manifest Document the requesting agent verified during pre-flight counterparty verification.
Intent-Assertion: detached JWT carrying principal-authorized purchase intent, forwardable to payment networks as standalone evidence.
Cart-Digest: digest of a structured cart returned by a prior QUOTE invocation, binding this PURCHASE to that cart.

Full field definitions, wire examples, and security requirements are in .

455 Counterparty Unverified (Summary) Receiving servers MUST return 455 Counterparty Unverified on PURCHASE invocations that fail merchant identity verification: missing Merchant-ID or Merchant-Manifest-Fingerprint headers, fingerprint mismatch, Merchant-ID mismatch, or a target merchant in any lifecycle state other than Active. 455 is a governance signal, parallel in role to 451 Scope Violation and 453 Zone Violation: MUST be logged; MUST NOT be retried without re-running counterparty verification.

Integration with PURCHASE, DISCOVER, and Attribution-Record Three existing AGTP primitives interact with merchant identity:

PURCHASE: Counterparty verification runs before PURCHASE is sent on the wire. A verified PURCHASE produces an Attribution- Record naming both the agent and the merchant cryptographically.
DISCOVER: The DISCOVER method defined in is extended by to return Merchant Manifest Documents when the query carries result_type: "merchant", and to return mixed agent/merchant result sets when result_type: "any". The existing DISCOVER signature model, ranking model, and governance-zone enforcement apply unchanged.
Attribution-Record: The Attribution-Record returned on PURCHASE includes merchant_id, merchant_fingerprint, and intent_assertion_jti fields when merchant identity binding is in effect. This produces a dual-party cryptographic record consumable by downstream audit and dispute-resolution processes without requiring those processes to speak AGTP.

Relationship to Payment Networks The merchant identity model defined in this document is payment-rail neutral. It does not define payment credential handling, tokenized card-on-file representations, authorization messaging to card networks, or settlement. Payment networks wishing to extend protection, fraud coverage, or dispute handling to agent-initiated transactions consume the Intent-Assertion JWT and the Attribution- Record as verifiable inputs to their own authorization and dispute flows; no AGTP-layer integration is required on the payment-network side. The specific mapping between AGTP merchant identity artifacts and payment-network message formats is expected to be defined bilaterally between governance platforms and individual networks and is out of scope for this document.

Security Considerations This section satisfies the mandatory IETF Security Considerations requirement. All AGTP implementations MUST address the considerations described here.

Mandatory TLS All AGTP connections MUST use TLS 1.3 or higher. Implementations MUST reject connections using TLS 1.2 or below. Certificate validation follows standard PKI practices per . Servers MUST present a valid certificate.

Agent Identity Verification: Three Levels AGTP defines three distinct levels at which agent identity and Authority-Scope can be verified. Each level serves a different deployment profile and operational tradeoff. Understanding the distinction is essential for implementers: the AGTP Agent Certificate extension () is OPTIONAL, and base AGTP provides cryptographic verification at the application layer without it. Level 1 - Self-asserted headers (raw request fields). Every AGTP request MUST include Agent-ID and Principal-ID header fields. As raw header values on an individual request, these fields are self-asserted: a client writes the values into the request and the server records what was written. Level 1 verification is limited to mandatory logging and anomaly detection against the recorded stream. This is the minimum baseline every AGTP implementation provides. Level 2 - Application-layer cryptographic verification (signed Agent Manifest Document). A canonical Agent-ID resolves to a signed Agent Manifest Document (Section 5.5) that carries the Birth Certificate's Authority-Scope grant and is signed by the governance platform that issued it. A verifier (including a stranger with no prior relationship to the agent's organization) can cryptographically verify identity and scope at the application layer by performing the following steps:

Resolve the canonical Agent-ID to retrieve the signed Agent Manifest Document.
Verify the governance platform's signature on the manifest against the platform's published key.
Confirm that the canonical Agent-ID in the manifest matches the hash of the Birth Certificate.
Read the Authority-Scope grant from the verified manifest.

Level 2 verification is available in base AGTP without the Agent Certificate extension. It is the identity mechanism the protocol depends on. Self-asserted headers (Level 1) are bound to verified identity (Level 2) by the resolver's retrieval of the signed manifest for the declared canonical Agent-ID. Level 3 - Transport-layer cryptographic verification (AGTP-CERT extension). The AGTP Agent Certificate extension binds Agent-ID, Principal-ID, and Authority-Scope to an X.509 v3 certificate presented during TLS 1.3 mutual authentication. Level 3 accelerates the Level 2 check to the TLS handshake and enables Scope-Enforcement Points (SEPs) to verify Authority-Scope at O(1) per-request cost without application-layer access. Level 3 is an acceleration and enforcement path for Level 2, not a replacement of it. Deployments that require line-rate scope enforcement at infrastructure layers (load balancers, governance gateways) SHOULD implement .

Note: The Agent Certificate extension and the Agent Birth Certificate mechanism may be subject to pending intellectual property claims. See Section 7.7 and the IPR Notice preceding the Abstract for details. The licensor is prepared to grant a royalty-free license to implementers.

Every AGTP server MUST log Agent-ID and Principal-ID fields for every request, creating an attributable audit trail at Level 1 even in deployments that do not implement Level 2 retrieval or Level 3 transport binding.

Authority Scope Enforcement The Authority-Scope header declares what actions the agent is authorized to take. Compliant AGTP servers MUST parse the Authority-Scope on every request, return 451 Scope Violation for any method that exceeds declared scope, and log all scope violations for audit purposes. At Level 1, scope declarations are self-asserted in the request header, analogous to scope assertions in OAuth 2.0 . At Level 2, scope is cryptographically verifiable through the signed Agent Manifest Document; servers SHOULD retrieve and verify the manifest for any Agent-ID whose declared scope exceeds read-only operations. Level 3 cryptographically signed and infrastructure-enforced scopes are defined in .

Threat Model

Agent Spoofing Threat: A malicious actor forges Agent-ID and Principal-ID headers to impersonate a trusted agent. Mitigation: Level 2 application-layer verification binds a declared Agent-ID to the signed Agent Manifest Document retrieved via canonical ID resolution. A forged Agent-ID either fails to resolve or resolves to a manifest whose signature cannot be verified against the claimed governance platform's published key. Level 3 raises the mitigation to the TLS handshake via . Implementations SHOULD retrieve and verify the manifest for any Agent-ID carrying scope beyond read-only query operations. Mandatory Level 1 logging provides an anomaly-detection baseline for deployments that do not perform active verification on every request.

Authority Laundering Threat: An agent claims an Authority-Scope broader than what it was granted. Mitigation: server-side scope enforcement; 451 Scope Violation returned and logged. In DELEGATE chains, each hop's scope MUST be a strict subset of the delegating agent's scope.

Delegation Chain Poisoning Threat: A malicious agent inserts itself into a DELEGATE chain. Mitigation: Delegation-Chain headers are logged at each hop. 551 Authority Chain Broken is returned if any chain entry is unverifiable. Full mitigation requires for signed delegation tokens.

Denial of Service via High-Frequency Agent Traffic Threat: Agents that are compromised, misconfigured, or adversarial generate extremely high request volumes. Mitigation: 429 Rate Limited status code. Rate limiting SHOULD be applied per Agent-ID and per Principal-ID. When is deployed, per-Agent-ID quotas can be cryptographically tied to verified identity, preventing quota evasion through Agent-ID spoofing.

Session Hijacking Threat: An attacker intercepts or forges a Session-ID. Mitigation: mandatory TLS protects sessions in transit. Session-IDs MUST be cryptographically random with minimum 128 bits of entropy. Servers MUST validate that Session-ID, Agent-ID, and TLS client identity are consistent.

Escalation Suppression Threat: A compromised agent or intermediary suppresses ESCALATE requests, preventing human oversight. Mitigation: compliant implementations MUST route ESCALATE requests directly to the declared escalation handler without modification. Intermediaries MUST NOT drop, delay, or modify ESCALATE requests. Escalation handlers SHOULD implement independent receipt confirmation.

Birth Certificate Spoofing Threat: A malicious actor fabricates a Birth Certificate to claim a legitimate agent's identity or construct a false identity with elevated trust. Mitigation: Birth Certificates are issued only by governance platforms that have completed one of the three Tier 1 verification paths (Section 5.2). For dns-anchored registrations, the governance platform MUST verify DNS ownership of the claimed org_domain before issuance. For log-anchored registrations, the governance platform MUST submit the Birth Certificate to a transparency log per / and record the inclusion proof in the registry; tampering with a log-anchored Birth Certificate is detectable by any party with log access. For hybrid registrations, both DNS and blockchain address ownership are verified. In the base spec, mandatory logging provides auditability. Full mitigation requires for cryptographically bound Birth Certificate verification at the transport layer. Governance platforms MUST treat any ACTIVATE request that presents a certificate hash matching an existing registry record as a collision attack and MUST reject it.

Domain Transfer Identity Hijacking Threat: An attacker acquires an expired domain to inherit the agent registry and trust history of prior registrants. Mitigation applies to dns-anchored and hybrid Tier 1 agents: agents under an expired domain are automatically Suspended within 24 hours of domain expiry detection. A new owner of the domain MUST NOT inherit prior agent registrations. See Section 9.6 for the full domain expiry policy. log-anchored Tier 1 agents are unaffected by this threat because their verification evidence is the transparency log inclusion proof rather than DNS ownership.

Attribution Forgery Threat: A malicious agent submits a fabricated or replayed Attribution-Record to claim credit for an action it did not perform, or to conceal the true execution context of an action it did perform. Mitigation: Attribution-Records MUST be signed with the agent's governance key. The signature MUST cover the full record including the Task-ID, Agent-ID, method, timestamp, and result hash. When is deployed, the signature is verified at the transport layer against the agent's X.509 certificate. For high-stakes domains, RATS attestation evidence in the Attribution-Record per provides hardware-rooted proof of execution context that cannot be forged without compromising the attesting environment itself. Attribution-Record signatures MUST be verified before the record is admitted to an audit trail. Unverified records MUST be logged with a signature_unverified flag and MUST NOT be treated as authoritative for compliance purposes.

Privacy Considerations Agent identity headers carry information about agent behavior that may be sensitive:

Agent-ID and Principal-ID together may reveal organizational structure
Session-ID and Task-ID reveal workflow patterns
Delegation-Chain reveals multi-agent architecture

AGTP logs containing these fields MUST be treated as sensitive operational data. Operators MUST implement appropriate access controls, retention limits, and data minimization practices consistent with applicable privacy regulations. Where privacy-preserving attribution is required, implementations MAY use pseudonymous Agent-IDs with a separate trusted resolution service. The architecture for pseudonymous agent identity resolution is reserved for a future companion document.

Denial-of-Service Considerations AGTP's agent identity headers provide a mechanism for more precise denial-of-service mitigation than is possible with HTTP. Rate limiting SHOULD be applied per Agent-ID and per Principal-ID in addition to per-IP-address controls. When is deployed, per-Agent-ID rate limiting can be cryptographically tied to verified agent identity, preventing quota evasion through Agent-ID rotation. Implementations planning high-volume governed agent deployments SHOULD plan for as part of their denial-of-service mitigation strategy. Additional recommended mitigations: Priority header enforcement (Priority: background requests SHOULD have lower rate limit headroom than Priority: critical); per-governance-zone aggregate limits in multi-tenant deployments; and circuit breaker patterns for ESCALATE request floods.

Intellectual Property Considerations The core AGTP specification, including all base methods, header fields, status codes, connection model, and IANA registrations defined in this document, is intended for open implementation without royalty obligation. Certain elements referenced in this document may be subject to pending patent applications by the author, specifically:

The Agent Certificate extension , which provides cryptographic binding of agent identity and authority scope to AGTP header fields.
The ACTIVATE method, which provides AGTP-native transmission and activation of governed agent packages.
The Agent Birth Certificate mechanism (Section 5.7), which provides the genesis identity record and canonical Agent-ID derivation process for AGTP-registered agents.
The .agent file format specification, an open packaging format for AI agents.
The .nomo file format specification, a governed packaging format for AI agents with cryptographic governance binding.

Implementers of the core AGTP specification are not affected by any intellectual property claims on these extensions and associated formats. The licensor is prepared to grant a royalty-free license to implementers for any patent claims that cover contributions in this document and its referenced extensions, consistent with the IETF's IPR framework under . IPR disclosures have been filed with the IETF Secretariat and are available at: https://datatracker.ietf.org/ipr/

IANA Considerations This document requests the following IANA actions upon advancement to RFC status.

Port Assignment Registration of the following service names in the IANA Service Name and Transport Protocol Port Number Registry: Proposed Port Assignments

Service Name	Port	Transport	Description
agtp	TBD	TCP	Agent Transfer Protocol over TCP/TLS
agtp-quic	TBD	UDP	Agent Transfer Protocol over QUIC

AGTP Method Registry Establishment of a new IANA registry: Agent Transfer Protocol Methods.

Registry name:: Agent Transfer Protocol Methods
Registration procedure:: Expert Review per , with the additional requirement that each registration be accompanied by a published specification, at minimum a publicly available Internet-Draft or equivalent document. The Designated Expert SHOULD verify that the proposed method name is unique, the reference specification is publicly accessible, and the method definition includes the required fields (parameters, response structure, idempotency, error codes, security considerations).
Reference:: This document

Initial registrations: Initial AGTP Method Registry Entries

Method	Status	Reference
QUERY	Permanent	This document, Section 7.2
SUMMARIZE	Permanent	This document, Section 7.2
BOOK	Permanent	This document, Section 7.2
SCHEDULE	Permanent	This document, Section 7.2
LEARN	Permanent	This document, Section 7.2
DELEGATE	Permanent	This document, Section 7.2
COLLABORATE	Permanent	This document, Section 7.2
CONFIRM	Permanent	This document, Section 7.2
ESCALATE	Permanent	This document, Section 7.2
NOTIFY	Permanent	This document, Section 7.2
DESCRIBE	Permanent	This document, Section 7.2
SUSPEND	Permanent	This document, Section 7.2

AGTP Status Code Registry Establishment of a new IANA registry: Agent Transfer Protocol Status Codes.

Registry name:: Agent Transfer Protocol Status Codes
Registration procedure:: Expert Review + published specification required.

The following AGTP-specific status codes are registered with full definitions: AGTP-Specific Status Code Definitions

Code	Name	Definition	Reference
451	Scope Violation	The requested action is outside the Authority-Scope declared in the request headers. The server MUST log this event. The agent MUST NOT retry the same request without modifying its Authority-Scope declaration. This is a governance signal, not a protocol error.	This document, Section 5.5
452	Budget Exceeded	The requested method execution would exceed the resource limits declared in the Budget-Limit request header. The agent MUST NOT retry without modifying the Budget-Limit or reducing request scope. This is a governance signal, not a protocol error. MUST be logged.	This document, Section 5.5
454	Grammar Violation	The method identifier fails AGIS grammar validation when `Method-Grammar: AGIS/1.0` is present. The response body MUST identify the specific AGIS validation pass that failed. The agent MUST NOT retry without correcting the method identifier.	This document, Section 6.4
261	Negotiation In Progress	The service has received a PROPOSE request and is evaluating the endpoint proposal. The response body MUST include a Negotiation-ID and an estimated evaluation duration. The agent MUST poll or wait for a 263 or rejection response.	This document, Section 6.5
262	Authorization Required for Negotiation	The service requires credential establishment before evaluating the PROPOSE request. The response body MUST specify the authorization mechanism required (e.g., AGTP-CERT, OAuth scope).	This document, Section 6.5
263	Endpoint Instantiated	The service has accepted the PROPOSE request and instantiated the requested endpoint. The response body MUST contain a complete AGIS endpoint definition for the instantiated endpoint. The Negotiation-ID MUST match the proposal.	This document, Section 6.5
460	Proposal Rejected	The service cannot or will not instantiate the proposed endpoint. The response body MUST explain the rejection reason and SHOULD reference relevant data_manifest entries if the requested data class is available through a different approach.	This document, Section 6.5
453	Zone Violation	The request would route outside the network boundary declared in the AGTP-Zone-ID header. SEP-enforced. The agent MUST NOT retry without modifying the AGTP-Zone-ID or obtaining explicit cross-zone authorization. MUST be logged.	This document, Section 5.5
455	Counterparty Unverified	The merchant counterparty in a PURCHASE invocation failed identity verification. Returned when the `Merchant-ID` or `Merchant-Manifest-Fingerprint` request headers are absent, when the fingerprint does not match the receiving server's current Merchant Manifest Document, when the Merchant-ID does not match the server's canonical ID, or when the merchant is in a non-Active lifecycle state. Governance signal; MUST be logged. Full definition in .	, Section 7
550	Delegation Failure	A sub-agent to which a task was delegated via the DELEGATE method failed to complete the task within the declared deadline or returned an error. The response body SHOULD contain the sub-agent's error details.	This document, Section 5.5
551	Authority Chain Broken	One or more entries in the Delegation-Chain header cannot be verified as part of a valid and continuous delegation sequence. The specific unverifiable entry SHOULD be identified in the response body. The server MUST log this event.	This document, Section 5.5

Header Field Registry AGTP header fields are distinct from HTTP header fields and are registered in a new IANA registry: Agent Transfer Protocol Header Fields.

Registry name:: Agent Transfer Protocol Header Fields
Registration procedure:: Expert Review + published specification required.

AGTP does not reuse the HTTP Field Name Registry, as AGTP header fields have different semantics, applicability, and versioning constraints from HTTP fields. HTTP header fields are not automatically valid in AGTP, and AGTP header fields are not valid HTTP fields. Initial registrations (all Permanent): AGTP-Version, AGTP-Method, AGTP-Status, Agent-ID, Principal-ID, Authority-Scope, Session-ID, Task-ID, Delegation-Chain, Priority, TTL, Server-Agent-ID, Attribution-Record, Continuation-Token, Supported-Methods, Budget-Limit, AGTP-Zone-ID, Content-Schema, Telemetry-Export, Cost-Estimate, Attestation-Evidence, Merchant-ID, Merchant-Manifest-Fingerprint, Intent-Assertion, Cart-Digest. The four merchant-related headers are defined in and registered concurrently with this document.

URI Scheme Registration Registration of the agtp:// URI scheme per , as described in Section 5.1.8 of this document.

AGTP Budget Unit Registry Establishment of a new IANA sub-registry: Agent Transfer Protocol Budget Units.

Registry name:: Agent Transfer Protocol Budget Units
Registration procedure:: Expert Review per . New unit registrations MUST define: unit name (lowercase ASCII, no spaces or special characters), semantic description, value format (integer or decimal), whether fractional values are permitted, and a reference specification. Units representing financial denominations MUST specify the currency and MUST define precision (decimal places). The Designated Expert SHOULD verify that the proposed unit does not duplicate an existing registration and that the value format is unambiguous.
Reference:: This document

Initial registrations: Initial AGTP Budget Unit Registry Entries

Unit	Description	Value Format	Fractional
tokens	Language model token consumption	Integer	No
compute-seconds	CPU/GPU compute time in seconds	Decimal	Yes
USD	US Dollar financial limit	Decimal, 2 places	Yes
EUR	Euro financial limit	Decimal, 2 places	Yes
GBP	Pound Sterling financial limit	Decimal, 2 places	Yes
calls	Downstream API call count	Integer	No

Agent Registry Retention Policy The AGTP registry MUST retain records for all registered agents regardless of lifecycle state. The following minimum retention periods apply: AGTP Registry Minimum Retention Periods

Lifecycle State	Minimum Retention Period
Active	Duration of Active state + 7 years
Suspended	Duration of Suspended state + 7 years
Revoked	10 years from revocation date
Deprecated	7 years from deprecation date

The 7-year minimum reflects common enterprise compliance requirements (SOX, GDPR audit trails, HIPAA). Governance platform operators in regulated industries SHOULD extend these minimums to match applicable regulatory requirements. The retained record for a Revoked or Deprecated agent MUST include:

Canonical Agent-ID (permanently retired, not reissued)
Agent label and org domain at time of registration
Trust tier at time of registration
Activation date and activating principal
Revocation or deprecation date, initiating principal, and reason code
Genesis audit record hash (pointer to immutable audit log)
Full Birth Certificate (archived, not publicly accessible)
All lifecycle state transitions with timestamps

The retained record MUST NOT contain package executable contents, active session data, or Authority-Scope grant tokens.

Domain Name Expiry Interaction If an organization's org_domain expires or transfers to a new owner:

All Active agents registered under the expired domain MUST be automatically Suspended within 24 hours of domain expiry detection.
The governance platform MUST notify the registered principal contact before suspension takes effect, with a minimum notice period of 30 days if domain expiry was predictable.
Suspended agents under an expired domain transition to Deprecated state after 90 days if the domain has not been renewed.
A new owner of the domain MUST NOT inherit prior agent registrations. New ACTIVATE transactions are required.

This policy prevents domain-transfer-based identity hijacking in which an attacker acquires an expired domain to claim the trust history of agents that operated under it.

References Normative References Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. QUIC: A UDP-Based Multiplexed and Secure Transport This document defines the core of the QUIC transport protocol. QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and network path migration. QUIC includes security measures that ensure confidentiality, integrity, and availability in a range of deployment circumstances. Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm. Using TLS to Secure QUIC This document describes how Transport Layer Security (TLS) is used to secure QUIC. HTTP Semantics The Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFCs 2818, 7231, 7232, 7233, 7235, 7538, 7615, 7694, and portions of 7230. Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] Guidelines for Writing an IANA Considerations Section in RFCs Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. Intellectual Property Rights in IETF Technology The IETF policies about Intellectual Property Rights (IPR), such as patent rights, relative to technologies developed in the IETF are designed to ensure that IETF working groups and participants have as much information as possible about any IPR constraints on a technical proposal as early as possible in the development process. The policies are intended to benefit the Internet community and the public at large, while respecting the legitimate rights of IPR holders. This document sets out the IETF policies concerning IPR related to technology worked on within the IETF. It also describes the objectives that the policies are designed to meet. This document updates RFC 2026 and, with RFC 5378, replaces Section 10 of RFC 2026. This document also obsoletes RFCs 3979 and 4879. Automatic Certificate Management Environment (ACME) Public Key Infrastructure using X.509 (PKIX) certificates are used for a number of purposes, the most significant of which is the authentication of domain names. Thus, certification authorities (CAs) in the Web PKI are trusted to verify that an applicant for a certificate legitimately represents the domain name(s) in the certificate. As of this writing, this verification is done through a collection of ad hoc mechanisms. This document describes a protocol that a CA and an applicant can use to automate the process of verification and certificate issuance. The protocol also provides facilities for other certificate management functions, such as certificate revocation. Remote ATtestation procedureS (RATS) Architecture In network protocol exchanges, it is often useful for one end of a communication to know whether the other end is in an intended operating state. This document provides an architectural overview of the entities involved that make such tests possible through the process of generating, conveying, and evaluating evidentiary Claims. It provides a model that is neutral toward processor architectures, the content of Claims, and protocols. Agentic Grammar and Interface Specification (AGIS) Informative References HTTP/3 The QUIC transport protocol has several features that are desirable in a transport for HTTP, such as stream multiplexing, per-stream flow control, and low-latency connection establishment. This document describes a mapping of HTTP semantics over QUIC. This document also identifies HTTP/2 features that are subsumed by QUIC and describes how HTTP/2 extensions can be ported to HTTP/3. Hypertext Transfer Protocol Version 2 (HTTP/2) This specification describes an optimized expression of the semantics of the Hypertext Transfer Protocol (HTTP), referred to as HTTP version 2 (HTTP/2). HTTP/2 enables a more efficient use of network resources and a reduced perception of latency by introducing header field compression and allowing multiple concurrent exchanges on the same connection. It also introduces unsolicited push of representations from servers to clients. This specification is an alternative to, but does not obsolete, the HTTP/1.1 message syntax. HTTP's existing semantics remain unchanged. The OAuth 2.0 Authorization Framework The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. This specification replaces and obsoletes the OAuth 1.0 protocol described in RFC 5849. [STANDARDS-TRACK] JSON Web Token (JWT) JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted. Guidelines and Registration Procedures for URI Schemes This document updates the guidelines and recommendations, as well as the IANA registration processes, for the definition of Uniform Resource Identifier (URI) schemes. It obsoletes RFC 4395. Certificate Transparency Version 2.0 This document describes version 2.0 of the Certificate Transparency (CT) protocol for publicly logging the existence of Transport Layer Security (TLS) server certificates as they are issued or observed, in a manner that allows anyone to audit certification authority (CA) activity and notice the issuance of suspect certificates as well as to audit the certificate logs themselves. The intent is that eventually clients would refuse to honor certificates that do not appear in a log, effectively forcing CAs to add all issued certificates to the logs. This document obsoletes RFC 6962. It also specifies a new TLS extension that is used to send various CT log artifacts. Logs are network services that implement the protocol operations for submissions and queries that are defined in this document. *** BROKEN REFERENCE *** Agent-to-Agent Protocol Specification Linux Foundation Agent Communication Protocol IBM Research Model Context Protocol Anthropic Agent Network Protocol AGTP Agent Certificate Extension AGTP Standard Extended Method Vocabulary Semantic Method Naming and LLM Agent Accuracy: A Controlled Benchmark of REST/CRUD versus Agentive API Interface Design AGTP Web3 Bridge Specification AGTP Agent Discovery and Name Service AGTP Composition with Agent Group Messaging Protocols AGTP Merchant Identity and Agentic Commerce Binding AGTP Transparency Log Protocol

Changes from v04 Version 05 restores the canonical Agent-ID as the primary identity primitive of AGTP and decouples Trust Tier 1 verification from DNS as a sole requirement. This undoes a drift introduced across v02 through v04 in which domain anchoring quietly became the operative trust root despite the v00 architecture establishing the canonical Agent-ID in that role.

Substantive Changes The following substantive changes were made:

The Foundational Principle (Section 5.1) has been rewritten to state explicitly that AGTP identity is agent-first and that all other identification forms are aliases resolving to a canonical Agent-ID.
The Canonical URI Forms have been expanded from four to five. Form 1 (canonical ID URI) is now explicitly marked authoritative. Form 2 restores the agent-native hierarchical namespace (agtp://[label].[org-label].agent) that was removed in the v04 response to the Web3 .agent TLD collision.
The v04 prohibition on .agent and .nomo in the hostname position has been removed. Namespace collision with Web3 naming systems is now handled through a deterministic resolution order (Section 5.1): AGTP registry first, Web3 second, canonical Agent-ID as authoritative tiebreaker. File format suffixes remain prohibited in the path position only.
Resolution Mechanics (Section 5.1) now defines two resolution paths: a Form 1 path that resolves canonical Agent-IDs via registry or transparency log lookup without requiring a domain anchor, and a Forms 2-5 path that resolves hierarchical and domain-anchored aliases through a governance platform registry lookup.
Trust Tier 1 verification has been decoupled from DNS. Section 5.2 now recognizes three equivalent verification paths: dns-anchored (RFC 8555 ACME challenge), log-anchored (Birth Certificate inclusion in a transparency log per RFC 9162 with optional RFC 9943 SCITT receipts), and hybrid (DNS control combined with blockchain address signature). All three paths produce identity attestations of equivalent strength for AGTP protocol purposes.
The Birth Certificate schema has added a verification_path field (REQUIRED for Tier 1) declaring which path was used at ACTIVATE time, an org_label field supporting Form 2 hierarchical resolution, and a log_inclusion_proof field (REQUIRED for log-anchored Tier 1). The org_domain field is downgraded from MUST to SHOULD, required only for the dns-anchored and hybrid paths.
The Agent Manifest Document now surfaces verification_path and log_inclusion_proof in the RECOMMENDED fields. The Tier 2 trust_warning value has changed from "org-label-unverified" to "verification-incomplete" to reflect that DNS is no longer the sole verification path.
The v04 Web3 Trust Anchors section has been rewritten. The resolution_layer field is replaced by verification_path. Web3 identity is no longer a degraded fallback capped at Tier 2; a Web3-anchored agent with a completed hybrid verification path is a full Tier 1 participant.
The IANA URI scheme registration (Section 5.1) has been updated to list all five URI forms with explicit syntax and semantics, and to state that the canonical Agent-ID form is the authoritative identity representation.
Threat Model entries for Birth Certificate Spoofing and Domain Transfer Identity Hijacking have been updated to reflect the multi-path model. Log-anchored Tier 1 agents are explicitly noted as unaffected by the domain-transfer threat.

Rationale The v04 architecture inverted the v00 intent by treating DNS ownership as the trust root and the canonical Agent-ID as a routing artifact. This created three specific problems that motivated the v05 revision: Stranger verification without prior relationship. In the v04 model, two agents from unrelated organizations with no shared DNS infrastructure had no first-class verification path. The v05 log-anchored path closes this gap: a stranger presented with a canonical Agent-ID and a transparency log inclusion proof can verify the Birth Certificate signature and read the Agent Manifest Document without resolving any domain. Cross-ecosystem transparency log interoperability. The v04 AGTP-CTL sketch referenced RFC 6962 (Certificate Transparency v1). The v05 log-anchored path targets RFC 9162 (CT v2) as the verifiable data structure with RFC 9943 (SCITT) COSE_Sign1 receipts for cross-ecosystem interoperability with deployed SCITT infrastructure. Identity stability across organizational change. A canonical Agent-ID derived from the Birth Certificate hash is stable across organizational renames, domain transfers, and resolution-path changes. Re-anchoring primary identity to DNS in v04 tied agent identity to a mutable external state (domain registration) that the v00 design subordinated to the canonical Agent-ID rather than treating as a primary anchor. Version 05 does not deprecate DNS-anchored verification. Implementations deployed on the v04 model continue to be Tier 1 compliant under the dns-anchored path. Version 05 expands the verification model rather than replacing it.

Authority-Scope Format Authority-Scope values are expressed as a space-separated list of scope tokens following the pattern: [domain]:[action] or [domain]:* for full domain access. Tokens MUST be lowercase ASCII with a single colon separator. Examples: Reserved domains (initial set): Reserved Authority-Scope Domains

Domain	Description
calendar	Scheduling and time-based resource management
documents	Document access, summarization, and annotation
knowledge	Agent context and memory operations
booking	Reservation and resource allocation
payments	Financial transactions and confirmations
agents	Delegation and collaboration with other agents
escalation	Escalation routing and handler management
activation	Governed agent package activation (ACTIVATE method extension)
discovery	Agent discovery and capability query operations (DISCOVER, DESCRIBE)
budget	Resource budget declaration and QUOTE pre-flight operations
telemetry	Telemetry export and observability operations
zone	Network zone boundary declaration and enforcement
suspend	Session suspension and resumption operations
merchant	Merchant identity resolution and counterparty verification (see )
intent	Intent Assertion issuance and validation (see )
*	All domains require explicit grant; use with caution

Example AGTP Wire Formats The following examples use a human-readable pseudo-wire format with HTTP-style headers followed by a JSON body. The Content-Type for all AGTP message bodies is application/agtp+json.

QUERY Request and Response

BOOK Request and Response

ESCALATE Request and Response

Comparison Table AGTP Compared to Existing Approaches

Criterion	AGTP	HTTP/REST	gRPC	AGMP (MCP, A2A, ...)
Intent-native methods	Yes (12 Tier 1)	No	No	Partial
Intent semantics at protocol level	Native	None	None	Messaging layer only
Built-in agent identity	Yes	No	No	No
Authority scope enforcement	Protocol-level	None	None	Application-layer
Built-in attribution/audit	Yes	No	No	Varies by impl.
Transport flexibility	TCP/UDP/QUIC	TCP/TLS	HTTP/2	HTTP
Escalation as first-class primitive	Yes	No	No	No
Ecosystem maturity	Proposed	Mature	Mature	Emerging
Governance/observability	Native	Manual/bolt-on	Manual	Limited
Method registry extensibility	Yes (Expert Review)	Frozen (IETF Review)	N/A	N/A
Open core / royalty-free	Yes	Yes	Yes	Yes
Agent Manifest Document	Native (.agtp format)	None	None	None
Tamper-proof identity surface	Yes (hash + signature)	No	No	No
Browser-accessible agent identity	Yes (read-only)	No	No	No
URI collision prevention	Domain-anchored	N/A	N/A	N/A
Agent Birth Certificate	Yes (genesis record)	No	No	No
Domain-expiry lifecycle handling	Specified	N/A	N/A	N/A
Capability discovery	Native (DESCRIBE)	None	Reflection (partial)	None
Resource budget enforcement	Native (Budget-Limit, 452)	None	None	None
Execution attestation (RATS)	Optional (RFC 9334)	None	None	None
Observability hooks	Native (Telemetry-Export)	None	None	None
Network zone enforcement	Native (AGTP-Zone-ID, 453)	None	None	None
Session suspension/recovery	Native (SUSPEND method)	None	None	None
AGMP composition profiles	Normative appendix	N/A	N/A	N/A

HTTP's method registry (registered with IETF Review per ) is effectively frozen for new semantic methods because any new HTTP method must be backward-compatible with existing HTTP infrastructure globally. AGTP's Expert Review + published spec procedure enables the protocol to evolve its method vocabulary as the agent ecosystem develops, without the backward-compatibility constraints of the HTTP method space.

Glossary

Agent:: A software system that executes tasks, makes decisions, and takes actions without continuous human supervision per transaction.
AGMP (Agent Group Messaging Protocol):: The collective term for higher-layer AI agent messaging standards that operate over AGTP as their transport substrate, including MCP, A2A, ACP, and ANP. AGMPs define what agents say. AGTP defines how those messages move. See Section 1.6.
Agent Birth Certificate:: A cryptographically signed identity document issued to an agent at registration time by a governance platform. The genesis record of the agent's existence; the source from which the canonical Agent-ID is derived. Functions as the agent's social security number: issued once, permanently bound, never reissued. See Section 6.7.
Agent Transfer Protocol (AGTP):: The application-layer protocol defined in this document, providing a dedicated transport environment for agent traffic.
Agent-ID:: A unique identifier for a specific agent instance, present in all AGTP request headers. In the base spec, derived from the Birth Certificate hash. With , cryptographically bound to a verified identity.
Agent Manifest Document:: A signed application/agtp+json document returned when an agtp:// URI is resolved. Derived from the agent's .agent or .nomo package. Contains identity, lifecycle state, trust tier, behavioral scope, and birth certificate fields. Never contains executable content.
AGTP-Zone-ID:: A request header declaring the network zone or organizational boundary within which a request must be processed. SEPs MUST enforce zone boundaries and return 453 Zone Violation if a DELEGATE or COLLABORATE request would route outside the declared zone.
Attribution Record:: A signed, logged record of an agent action, sufficient for audit and compliance purposes. MAY include RATS attestation evidence per for hardware-rooted execution proof in high-stakes domains.
Authority-Scope:: A declared set of permissions defining what actions an agent is authorized to take, expressed as space-separated domain:action tokens.
Budget-Limit:: A request header declaring the maximum resource consumption the principal authorizes for a method invocation, expressed as space-separated unit=value tokens from the IANA AGTP Budget Unit Registry. Exceeding the declared limit causes 452 Budget Exceeded.
Delegation Chain:: An ordered record of Agent-IDs representing the sequence of delegations that led to the current request.
DESCRIBE:: An AGTP Tier 1 core method returning the declared capabilities, supported modalities, method vocabulary, and versioned feature set of a specific agent endpoint. Used for pre-task negotiation. Category: ACQUIRE.
ESCALATE:: An AGTP method representing an agent's intentional deferral of a decision or action to a human principal or higher-authority agent. A first-class method, not a failure code.
Governance Token:: A signed, time-limited JWT artifact encoding a specific governance verdict for a specific action. The runtime companion to the Birth Certificate. Default TTL: 30 seconds. Must not be reused.
Intent Verb:: An AGTP method name expressing the agent's purpose, as distinguished from HTTP resource-operation verbs (GET, POST, PUT, DELETE).
Method Registry:: The IANA-maintained registry of valid AGTP method names and their specifications. Registration requires Expert Review and a published specification.
Principal:: The human, organization, or system that authorized an agent to act and is accountable for its actions.
Principal-ID:: The identifier of the principal on whose behalf an agent operates, present in all AGTP request headers.
Scope-Enforcement Point (SEP):: An AGTP-aware infrastructure component, load balancer, gateway, proxy, that enforces Authority-Scope and AGTP-Zone-ID compliance on AGTP requests without application-layer access. Requires .
Scope Violation (451):: An AGTP status code returned when an agent requests an action outside its declared Authority-Scope. A governance signal, not a protocol error. MUST be logged.
Session:: An AGTP persistent connection context shared across multiple method invocations within a single agent workflow.
SUSPEND (method):: An AGTP Tier 1 core method that places a specific active session into a recoverable paused state, issuing a single-use base64url-encoded 128-bit resumption nonce. Session-scoped; does not affect registry lifecycle state. Category: ORCHESTRATE.
Trust Tier:: A classification (1, 2, or 3) assigned to an agent at registration based on the strength of identity verification. Tier 1 requires one of three verification paths (DNS-anchored, log-anchored, or hybrid) and a .nomo governed package. Tier 2 is org-asserted without cryptographic verification. Tier 3 is experimental, not production-eligible.
551 Authority Chain Broken:: An AGTP status code returned when one or more entries in the Delegation-Chain header cannot be verified as part of a valid and continuous delegation sequence. MUST be logged.

AGTP Composition with AGMPs This appendix provides normative mapping guidance for carrying AGMP messages (MCP, A2A, ACP) over AGTP as their transport substrate. Full composition specifications are provided in ; this appendix provides the canonical mapping table and precedence rules.

Precedence Rule AGTP headers (Agent-ID, Principal-ID, Authority-Scope, Delegation-Chain) take precedence over equivalent fields in the messaging-layer payload for routing, enforcement, and audit purposes. Infrastructure components including SEPs and governance gateways MUST use AGTP header values for all protocol-level decisions. Messaging-layer identity fields MAY be present in the body for application-layer use but MUST NOT override AGTP header values.

AGMP-to-AGTP Canonical Mapping AGMP-to-AGTP Canonical Mapping

AGMP	Concept	AGTP Mapping
A2A	Task	AGTP DELEGATE body; A2A `task.id` maps to Task-ID header
A2A	Capability	AGTP DESCRIBE response; `capability_domains`
A2A	Agent Card	AGTP Agent Manifest Document
A2A	Provenance chain	AGTP Delegation-Chain header
A2A	Artifact	AGTP NOTIFY body with `content_type: artifact`
MCP	Tool call	AGTP QUERY or NOTIFY body
MCP	Context / conversation state	AGTP Session-ID header + LEARN method
MCP	Sampling / inference request	AGTP QUERY with `modality: inference`
MCP	Resource	AGTP QUERY with appropriate `scope`
ACP	Agent-to-agent message	AGTP NOTIFY or COLLABORATE body
ACP	Capability advertisement	AGTP DESCRIBE response

Wire Example: A2A Task over AGTP

Wire Example: MCP Tool Call over AGTP