Internet-Draft api-catalog May 2023
Smith Expires 13 November 2023 [Page]
Internet Engineering Task Force
Intended Status:
Standards Track
K. Smith, Ed.

api-catalog: A well-known URI to help discovery of APIs


This document defines the "api-catalog" well-known URI. It is intended to facilitate discovery of the APIs published by a Web host.

Status of This Memo

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This Internet-Draft will expire on 13 November 2023.

Table of Contents

1. Introduction

A Web host may publish Application Programming Interfaces (APIs) to encourage requests for interaction from external parties. Such APIs must be discovered before they may be used - i.e., the external party needs to know what APIs a given Web host exposes, including their purpose, any constraints to use, and the endpoints to interact with the APIs. To faciliate discovery of this information, this document proposes a well-known URI, 'api-catalog', as a location where a Web host's API endpoints are listed and described.

1.1. Goals and non-goals

The primary goal is to facilitate the discovery of both a Web Host's public API endpoints, and metadata that informs the potential API client of the purpose of each API and any constraints around usage.

Non-goals: this document does not mandate paths for API endpoints. i.e., it does not mandate that my_example_api should be available at (although it is not forbidden to do so).

1.2. Requirements Language

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] when, and only when, they appear in all capitals, as shown here.

2. Using the 'api-catalog' well-known URI

The api-catalog well-known URI is intended for HTTP(S) servers that publish APIs and wish to facilitate their discovery. Since the purpose of the api-catalog well-known URI is to facilitate API discovery with minimal prior knowledge, it is recommended that /.well-known/api-catalog be hosted at a predictable hostname, i.e. . It may also be hosted at other hostnames, e.g., etc.

A Web host ( supporting this URI:

3. Associated Media type: the api-catalog linkset

A request to the api-catalog well-known URI is expected to return a set of one or more links, each labelled with a link relation to allow machines and humans to decide if, and understand why, to follow them. The api-catalog is recommended to consist of:

[RFC9264] defines the application/linkset+json JSON document format for link sets, and is used for the following example:

{ "linkset":
        { "anchor": "",
          "api-portal": [
                {"href": ""}
        { "anchor": ",
          "" : [
                {"href": ""}
        { "anchor": ",
          "" : [
                {"href": ""}
        { "anchor": ",
          "" : [
                {"href": ""}

Figure 1: api-catalog linkset example

5. Conformance to RFC8615

The requirements in section 3 of [RFC8615] for defining Well-Known Uniform Resource Identifiers are met as follows:

5.1. Path prefix

The api-catalog URI SHALL be appended to the /.well-known/ path-prefix for "well-known locations".

5.2. Supported URI schemes

The api-catalog well-known URI may be used with the HTTP and HTTPS URI schemes.

5.3. Registration of the api-catalog well-known URI

See Section 6 considerations below.

6. IANA Considerations

6.1. The api-catalog well-known URI

This specification registers the "api-catalog" well-known URI in the Well-Known URI Registry as defined by [RFC6415] .

URI suffix: api-catalog

Specification document(s): draft-smith-api-catalog-01

Related information: The "api-catalog" documents obtained from the same host using the HTTP and HTTPS protocols (using default ports) MUST be identical.

This specification registers the "api-catalog" link relation by following the procedures per section 4.2.2 of [RFC8288] (Editor's note: this is TODO).

(Editor's note: if the suggestion above to include this is agreed).

7. Security Considerations


8. References

8.1. Normative References

Hammer-Lahav, E., Ed. and B. Cook, "Web Host Metadata", RFC 6415, DOI 10.17487/RFC6415, , <>.
Nottingham, M., "Web Linking", RFC 8288, DOI 10.17487/RFC8288, , <>.
Nottingham, M., "Well-Known Uniform Resource Identifiers (URIs)", RFC 8615, DOI 10.17487/RFC8615, , <>.
Wilde, E. and H. Van de Sompel, "Linkset: Media Types and a Link Relation Type for Link Sets", RFC 9264, DOI 10.17487/RFC9264, , <>.

8.2. Informative References

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.



Author's Address

Kevin Smith (editor)
One Kingdom Street
W2 6BY
United Kingdom