REST API Media Types
draft-ietf-httpapi-rest-api-mediatypes-08

HTTPAPI                                                         R. Polli
Internet-Draft                                                   Par-Tec
Intended status: Informational                           4 November 2025
Expires: 8 May 2026

                          REST API Media Types
               draft-ietf-httpapi-rest-api-mediatypes-08

Abstract

   This document registers the following media types used in APIs on the
   IANA Media Types registry: application/openapi+json, and application/
   openapi+yaml.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-httpapi-rest-api-
   mediatypes/.

   Discussion of this document takes place on the HTTPAPI Working Group
   mailing list (mailto:httpapi@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/httpapi/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/httpapi/.  Working Group
   information can be found at https://datatracker.ietf.org/wg/httpapi/
   about/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ietf-wg-httpapi/mediatypes/labels/rest-api.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on 8 May 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Media Type registrations  . . . . . . . . . . . . . . . . . .   3
     2.1.  The OpenAPI Media Types . . . . . . . . . . . . . . . . .   3
       2.1.1.  Media Type application/openapi+json . . . . . . . . .   3
       2.1.2.  Media Type application/openapi+yaml . . . . . . . . .   5
   3.  Interoperability Considerations . . . . . . . . . . . . . . .   6
     3.1.  Using the version parameter . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
     4.1.  General Considerations  . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   8
   FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Change Log  . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     Since -00 . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     Since -04 . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   OpenAPI Specification [OAS] version 3 and above is a consolidated
   standard for describing HTTP APIs using the JSON [JSON] and YAML
   [YAML] data format.

   To increase interoperability when processing API descriptions and
   leverage content negotiation mechanisms when exchanging OpenAPI
   description representations this specification registers the
   following media types: application/openapi+json and application/
   openapi+yaml.

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1.1.  Notational Conventions

   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.  These words may also appear in this
   document in lower case as plain English words, absent their normative
   meanings.

   The terms "content", "content negotiation", "resource", and "user
   agent" in this document are to be interpreted as in [HTTP].

2.  Media Type registrations

   This section describes the information required to register the above
   media types according to [MEDIATYPE].

2.1.  The OpenAPI Media Types

   The OpenAPI Specification Media Types convey semantics for OpenAPI
   Document (OAD) resources as defined in [OAS] for version 3.0 and
   above.

   Those resources can be represented in [JSON] or [YAML].  Since there
   are multiple OpenAPI Specification versions, those media types
   support the version parameter.

   The following example conveys the desire of a client to receive an
   OpenAPI Document resource based on the stated preferences:

   1.  openapi 3.1 in YAML

   2.  openapi 3.0 in YAML

   3.  any openapi version in JSON

   Accept: application/openapi+yaml;version=3.1,
           application/openapi+yaml;version=3.0;q=0.5,
           application/openapi+json;q=0.3

2.1.1.  Media Type application/openapi+json

   The following information serves as the registration form for the
   application/openapi+json media type.

   Type name:  application

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   Subtype name:  openapi+json

   Required parameters:  None

   Optional parameters:  version: its value is a string representing the
      OpenAPI Specification version. ; unrecognized parameters should be
      ignored

   Encoding considerations:  Same as "application/json"

   Security considerations:  See Section 4 of this document,
      "application/json" and [OAS]

   Interoperability considerations:  See Section 3 of this document,
      "application/json" and [OAS]

   Published specification:  this document, [OAS]

   Applications that use this media type:  HTTP

   Fragment identifier considerations:  [OAS] or the specific version of
      the OpenAPI document.

   Additional information:

   *  Deprecated alias names for this type: "application/
      vnd.oai.openapi+json".  This name is used, but not registered.

   *  Magic number(s): N/A

   *  File extension(s): json

   *  Macintosh file type code(s): N/A

   Person and email address to contact for further information:  See Aut
      hors' Addresses section.

   Intended usage:  COMMON

   Restrictions on usage:  None.

   Author:  See Authors' Addresses section.

   Change controller:  IETF

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2.1.2.  Media Type application/openapi+yaml

   The following information serves as the registration form for the
   application/openapi+yaml media type.

   Type name:  application

   Subtype name:  openapi+yaml

   Required parameters:  N/A

   Optional parameters:  version: its value is a string representing the
      OpenAPI Specification version. ; unrecognized parameters should be
      ignored

   Encoding considerations:  Same as "+yaml" Structured Syntax Suffix

   Security considerations:  See Section 4 of this document, "+yaml"
      Structured Syntax Suffix and [OAS]

   Interoperability considerations:  See Section 3 of this document,
      "+yaml" Structured Syntax Suffix and [OAS]

   Published specification:  [OAS]

   Applications that use this media type:  HTTP

   Fragment identifier considerations:  [OAS] or the specific version of
      the OpenAPI document.

   Additional information:

   *  Deprecated alias names for this type: "application/
      vnd.oai.openapi".  This name is used, but not registered.

   *  Magic number(s): N/A

   *  File extension(s): Same as "application/yaml"

   *  Macintosh file type code(s): N/A

   Person and email address to contact for further information:  See Aut
      hors' Addresses section

   Intended usage:  COMMON

   Restrictions on usage:  None.

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   Author:  See Authors' Addresses section

   Change controller:  IETF

3.  Interoperability Considerations

   Interoperability requirements for media type registrations are
   discussed in Section 4.6 of [MEDIATYPE] and in the Interoperability
   Considerations of the "+yaml" Structured Syntax Suffix.

3.1.  Using the version parameter

   The version parameter ought to be processed according with the
   associated OpenAPI Specification.

   For example, when an OpenAPI 3.1 resource uses the patch version
   version=3.1.1, its value is expected to be ignored by tooling (see
   https://spec.openapis.org/oas/v3.1.0.html#versions).

4.  Security Considerations

   Security requirements for media type registrations are discussed in
   Section 4.6 of [MEDIATYPE]. and in the Security Considerations of the
   "+yaml" Structured Syntax Suffix.

4.1.  General Considerations

   OpenAPI documents are processed by a wide variety of tooling for
   numerous different purposes, such as client code generation,
   documentation generation, server side routing, and API testing.
   OpenAPI document authors must consider the risks of the scenarios
   where the OpenAPI document may be used.

   An OpenAPI document describes the security schemes used to protect
   the resources it defines.  The security schemes available offer
   varying degrees of protection.  Factors such as the sensitivity of
   the data and the potential impact of a security breach should guide
   the selection of security schemes for the API resources.  Some
   security schemes, such as basic auth and OAuth Implicit flow, are
   supported for compatibility with existing APIs.  However, their
   inclusion in OpenAPI does not constitute an endorsement of their use,
   particularly for highly sensitive data or operations.

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   OpenAPI documents may contain references to external resources that
   may be dereferenced automatically by consuming tools.  External
   resources may be hosted on different domains that may be untrusted.
   References in an OpenAPI document, or across OpenAPI documents may
   cause a cycle.  Tooling must detect and handle cycles to prevent
   resource exhaustion.

   Certain properties allow the use of Markdown which can contain HTML
   including script.  It is the responsibility of tooling to
   appropriately sanitize the Markdown.

   OpenAPI documents use [jsonschema] therefore share the security
   consideration of JSON Schema.

5.  IANA Considerations

   This specification defines the following new Internet media types
   [MEDIATYPE].

   IANA is asked to update the "Media Types" registry at
   https://www.iana.org/assignments/media-types
   (https://www.iana.org/assignments/media-types) with the registration
   information provided in the sections below.

      +==========================+==================================+
      | Media Type               | Registration information section |
      +==========================+==================================+
      | application/openapi+json | Section 2.1.1 of this document   |
      +--------------------------+----------------------------------+
      | application/openapi+yaml | Section 2.1.2 of this document   |
      +--------------------------+----------------------------------+

                                  Table 1

6.  Normative References

   [HTTP]     Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9110>.

   [JSON]     Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/rfc/rfc8259>.

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   [jsonschema]
              Wright, A., Andrews, H., Hutton, B., and G. Dennis, "JSON
              Schema", 28 January 2020,
              <https://json-schema.org/specification.html>.

   [MEDIATYPE]
              Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/rfc/rfc6838>.

   [OAS]      Darrel Miller, Jeremy Whitlock, Marsh Gardiner, Mike
              Ralphson, Ron Ratovsky, and Uri Sarid, "OpenAPI
              Specification 3.1.0", 15 February 2021,
              <https://spec.openapis.org/oas/latest>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.

   [YAML]     Oren Ben-Kiki, Clark Evans, and Ingy dot Net, "YAML Ain't
              Markup Language Version 1.2", 1 October 2021,
              <https://yaml.org/spec/1.2/spec.html>.

Acknowledgements

   Thanks to Erik Wilde and David Biesack for being the initial
   contributors of this specification, and to Darrel Miller and Rich
   Salz for their support during the adoption phase.

   In addition to the people above, this document owes a lot to the
   extensive discussion inside and outside the HTTPAPI workgroup.  The
   following contributors have helped improve this specification by
   opening pull requests, reporting bugs, asking smart questions,
   drafting or reviewing text, and evaluating open issues:

   Austin Wright, Ben Hutton and Jason Desrosiers.

FAQ

   This section is to be removed before publishing as an RFC.

   Q: Why this document?  After all these years, we still lack a proper

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      media type for REST related document types.  This has some
      security implications too (eg. wrt on identifying parsers or treat
      downloads)

Change Log

   This section is to be removed before publishing as an RFC.

   RFC EDITOR PLEASE DELETE THIS SECTION.

Since -00

   This section is to be removed before publishing as an RFC.

   *  Split YAML registrations in a separate I-D.

Since -04

   This section is to be removed before publishing as an RFC.

   *  Split JSONSCHEMA registrations in a separate I-D.

Author's Address

   Roberto Polli
   Par-Tec
   Italy
   Email: robipolli@gmail.com

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