| Internet-Draft | Well-Known URIs | February 2026 |
| Nottingham | Expires 27 August 2026 | [Page] |
This memo defines a path prefix for "well-known locations",
"/.well-known/", in selected Uniform Resource Identifier (URI) schemes.¶
In doing so, it obsoletes RFC 8615.¶
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
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This Internet-Draft will expire on 27 August 2026.¶
Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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Some applications on the Web require the discovery of information about an origin [RFC6454] (sometimes called "site-wide metadata") before making a request. For example, the Robots Exclusion Protocol [RFC9309] specifies a way for automated processes to obtain permission to access resources; likewise, the Platform for Privacy Preferences [P3P] tells user agents how to discover privacy policy before interacting with an origin server.¶
While there are several ways to access per-resource metadata (e.g., HTTP header fields, PROPFIND in Web Distributed Authoring and Versioning (WebDAV) [RFC4918]), the perceived overhead (either in terms of client-perceived latency and/or deployment difficulties) associated with them often precludes their use in these scenarios.¶
At the same time, it has become more popular to use HTTP as a substrate for non-Web protocols. Sometimes, such protocols need a way to locate one or more resources on a given host.¶
When this happens, one solution is to designate a "well-known location" for data or services related to the origin overall, so that it can be easily located. However, this approach has the drawback of risking collisions, both with other such designated "well-known locations" and with resources that the origin has created (or wishes to create). Furthermore, defining well-known locations usurps the origin's control over its own URI space [RFC7320].¶
To address these uses, this memo reserves a path prefix in nominated URI schemes for these "well-known locations", "/.well-known/". Future specifications that need to define a resource for such metadata can register their use to avoid collisions and minimise impingement upon origins' URI space.¶
Well-known URIs can also be used with other URI schemes, but only when those schemes' definitions explicitly allow it.¶
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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
A well-known URI is a URI [RFC3986] whose path component begins with the characters "/.well-known/", provided that the scheme is explicitly defined to support well-known URIs.¶
For example, if an application registers the name 'example', the corresponding well-known URI on 'http://www.example.com/' would be 'http://www.example.com/.well-known/example'.¶
Previous revisions of this specification updated the "http" [RFC9110] and "https" [RFC9110] schemes to support well-known URIs. Other existing schemes can use the appropriate process for updating their definitions; for example, [RFC8307] does so for the "ws" and "wss" schemes. The "Uniform Resource Identifier (URI) Schemes" registry tracks which schemes support well-known URIs.¶
Applications that wish to mint new well-known URIs MUST register them, following the procedures in Section 5.1, subject to the following requirements.¶
Registered names MUST conform to the "segment-nz" production in [RFC3986]. This means they cannot contain the "/" character.¶
Registered names for a specific application SHOULD be correspondingly precise; "squatting" on generic terms is not encouraged. For example, if the Example application wants a well-known location for metadata, an appropriate registered name might be "example-metadata" or even "example.com-metadata", not "metadata".¶
At a minimum, a registration will reference a specification that defines the format and associated media type(s) to be obtained by dereferencing the well-known URI, along with the URI scheme(s) that the well-known URI can be used with. If no URI schemes are explicitly specified, "http" and "https" are assumed.¶
Typically, applications will use the default port for the given scheme; if an alternative port is used, it MUST be explicitly specified by the application in question.¶
Registrations MAY also contain additional information, such as the syntax of additional path components, query strings, and/or fragment identifiers to be appended to the well-known URI, or protocol-specific details (e.g., HTTP [RFC9110] method handling).¶
Note that this specification defines neither how to determine the hostname to use to find the well-known URI for a particular application, nor the scope of the metadata discovered by dereferencing the well-known URI; both should be defined by the application itself.¶
Also, this specification does not define a format or media type for the resource located at "/.well-known/", and clients should not expect a resource to exist at that location.¶
Well-known URIs are rooted in the top of the path's hierarchy; they are not well-known by definition in other parts of the path. For example, "/.well-known/example" is a well-known URI, whereas "/foo/.well-known/example" is not.¶
See also Section 4 for Security Considerations regarding well-known locations.¶
The "Well-Known URIs" registry is located at <https://www.iana.org/assignments/well-known-uris/>. Registration requests can be made by following the instructions located there or by sending an email to the <wellknown-uri-review@ietf.org> mailing list.¶
Registration requests consist of at least the following information:¶
The name requested for the well-known URI, relative to "/.well-known/"; e.g., "example". Syntactic requirements are described in Section 3.¶
For Standards Track RFCs, state "IETF". For others, give the name of the responsible party. Other details (e.g., email address, home page URI) may also be included.¶
Reference to the document that specifies the field, preferably including a URI that can be used to retrieve a copy of the document. An indication of the relevant sections may also be included, but is not required. Specification documents are expected to address the security considerations in Section 4.¶
One of "permanent", "provisional", "obsoleted", or "deprecated". See guidance below.¶
Optionally, citations to additional documents containing further relevant information.¶
Values defined by Standards Track RFCs and other open standards (in the sense of [RFC2026], Section 7.1.1) can be registered with a status of "permanent".¶
The change controller of a permanent registration MUST be the responsible party for the specification document(s). The change controller of a permanent registration can request that its status be changed to "obsoleted" or "deprecated" as circumstances require. If a change controller becomes defunct or cannot be contacted, the experts can change a registration's status as required, in consultation with the community.¶
Values not defined by open standards processes can be registered with a status of "provisional".¶
A request for provisional registration can be denied by the experts if they find that it uses a URI suffix that is overly generic or of potential community value in the future. For example, a provisional registration request for a commonly used term can be denied on the basis that it could preempt a future standards effort's use of the term, even if no such effort is yet in progress.¶
Provisional entries can be promoted to "permanent" by the experts if -- in consultation with the community -- the experts find they are in broad use.¶
Provisional entries can be removed by the experts if -- in consultation with the community -- the experts find that they are not in broad use one year or more after registration.¶
Provisional entries can be removed by the experts at any time if the specification document(s) become unavailable, deprecated, obsoleted, or similar. In the case that a document becomes unavailable, the experts must attempt contact with the change controller to clarify its status first.¶
Note that "consult the community" above refers to those responsible for the URI scheme(s) in question. Generally, this would take place on the mailing list(s) of the appropriate Working Group(s) (possibly concluded), or on <art@ietf.org> if no such list exists.¶
The experts will keep public records of their decisions. Decisions by the experts can be appealed to the IESG.¶
Applications minting new well-known URIs, as well as administrators deploying them, will need to consider several security-related issues, including (but not limited to) exposure of sensitive data, denial-of-service attacks (in addition to normal load issues), server and client authentication, vulnerability to DNS rebinding attacks, and attacks where limited access to a server grants the ability to affect how well-known URIs are served.¶
[RFC3552] contains some examples of potential security considerations that may be relevant to application protocols and administrators deploying them.¶
Because well-known locations effectively represent the entire origin, server operators should appropriately control the ability to write to them. This is especially true when more than one entity is
co-located on the same origin. Even for origins that are controlled by and represent a single entity, due care should be taken to assure that write access to well-known locations is not granted unwittingly, either externally through server configuration or locally through implementation permissions (e.g., on a filesystem).¶
Applications using well-known URIs for "http" or "https" URLs need to be aware that well-known resources will be accessible to Web browsers, and therefore are able to be manipulated by content obtained from other parts of that origin. If an attacker is able to inject content (e.g., through a Cross-Site Scripting vulnerability), they will be able to make potentially arbitrary requests to the well-known resource.¶
HTTP and HTTPS also use origins as a security boundary for many other mechanisms, including (but not limited to) cookies [RFC6265], Web Storage [WEBSTORAGE], and various capabilities.¶
An application that defines well-known locations should not assume that it has sole access to these mechanisms or that it is the only application using the origin. Depending on the nature of the application, mitigations can include:¶
Encrypting sensitive information¶
Allowing flexibility in the use of identifiers (e.g., cookie names) to avoid collisions with other applications¶
Using the 'HttpOnly' flag on cookies to assure that cookies are not exposed to browser scripting languages [RFC6265]¶
Using the 'Path' parameter on cookies to assure that they are not available to other parts of the origin [RFC6265]¶
Using X-Content-Type-Options: nosniff [FETCH] to assure that content under attacker control can't be coaxed into a form that is interpreted as active content by a Web browser¶
Other good practices include:¶
Using an application-specific media type in the Content-Type header field, and requiring clients to fail if it is not used¶
Using Content-Security-Policy [CSP] to constrain the capabilities of active content (such as HTML [HTML5]), thereby mitigating Cross-Site Scripting attacks¶
Using Referrer-Policy [REFERRER-POLICY] to prevent sensitive data in URLs from being leaked in the Referer request header field¶
Avoiding use of compression on any sensitive information (e.g., authentication tokens, passwords), as the scripting environment offered by Web browsers allows an attacker to repeatedly probe the compression space; if the attacker has access to the path of the communication, they can use this capability to recover that information.¶
This memo does not specify the scope of applicability for the information obtained from a well-known URI, and does not specify how to discover a well-known URI for a particular application.¶
Individual applications using this mechanism must define both aspects; if this is not specified, security issues can arise from implementation deviations and confusion about boundaries between applications.¶
Applying metadata discovered in a well-known URI to resources other than those co-located on the same origin risks administrative as well as security issues. For example, allowing "https://example.com/.well-known/example" to apply policy to "https://department.example.com", "https://www.example.com", or even "https://www.example.com:8000" assumes a relationship between hosts where there might be none, thereby giving control to a potential attacker.¶
Likewise, specifying that a well-known URI on a particular hostname is to be used to bootstrap a protocol can cause a large number of undesired requests. For example, if a well-known HTTPS URI is used to find policy about a separate service such as email, it can result in a flood of requests to Web servers, even if they don't implement the well-known URI. Such undesired requests can resemble a denial-of-service attack.¶
This specification updates the registration procedures for the "Well-Known URI" registry, first defined in [RFC5785].¶
Well-known URIs are registered on the advice of one or more experts, with a Specification Required (using terminology from [RFC8126]).¶
See Section 3.1 for the registration request procedure.¶
IANA will direct the senders of any incoming registry requests to this document and, if defined, the processes established by the expert(s); typically, this will mean referring them to the registry Web page.¶
They are, but for various reasons -- both technical and social -- they are sometimes necessary. This memo defines a "sandbox" for them, to reduce the risks of collision and to minimise the impact upon preexisting URIs on sites.¶
It's short, descriptive, and according to search indices, not widely used.¶
None, until they choose to use this mechanism.¶
Allowing every URI path segment to have a well-known location (e.g., "/images/.well-known/") would increase the risks of colliding with a preexisting URI on a site, and generally these solutions are found not to scale well because they're too "chatty".¶
Updated registration guidelines¶