API Catalog

RFC 9727 /.well-known/api-catalog lets agents discover available APIs.

Category: Protocol discovery
Standard: Recommended

1%Top 100 adoption1 of 93 sites implement it 4/9OverviewSpeculativeSpecified, but little evidence anything uses it yet.

Who supports it

No agent or browser has announced support yet.

27 others: no evidence yet. See every agent and browser

What it checks

The extension fetches /.well-known/api-catalog, the location RFC 9727 defines for a list of a publisher’s APIs. It passes when the response is successful, non-empty, and JSON: the Content-Type mentions json (RFC 9727 uses application/linkset+json), or the body starts with { or [. The contents are not otherwise validated.

Results

Status	When
Pass	`/.well-known/api-catalog` returns a JSON document
N/A	The path is missing or does not return JSON

How to fix

If you publish APIs, serve a linkset at /.well-known/api-catalog that links to each API’s description documents:

{
  "linkset": [
    {
      "anchor": "https://api.example.com/v1",
      "service-desc": [
        { "href": "https://api.example.com/v1/openapi.json", "type": "application/json" }
      ],
      "service-doc": [{ "href": "https://example.com/docs/api", "type": "text/html" }]
    }
  ]
}

Serve it with Content-Type: application/linkset+json.

Support by agent and browser

Announced means the vendor’s own docs or announcement say so. Published is the date on the vendor’s own page, where it has one. Checked is the last time our weekly research found that page still saying so.

No agent or browser has announced anything about this yet.

No evidence yet27

ChatGPT
Claude
Gemini
Perplexity
Copilot
Meta AI
ChatGPT Atlas
Comet
Dia
Gemini in Chrome
Edge Copilot Mode
Claude Code
Cursor
Codex
GitHub Copilot
Windsurf
CCBot
Applebot
Amazonbot
Bytespider
Cohere
Mistral
DuckAssist
Chrome
Edge
Firefox
Safari

Names and marks belong to their owners and are used only to identify products. None of these vendors is affiliated with Sitebulb. Spotted something out of date? Send a correction.

Adoption on the top 100 sites

1 of 93 measured sites implement it

Scanned 23 Oct 2026 with the Sitebulb Labs extension, against the Tranco list (tranco-56Z8N). 7 sites couldn’t be measured (bot challenge or timeout) and are left out of the share.

9 Oct 2026 2% → 23 Oct 2026 1%

Sites implementing it1

#106 sentry.io

Overview

4/9

Speculative

Specified, but little evidence anything uses it yet.

How this rating is worked out4 of 9 points

Factor	Points	Why
Vendor support	0 / 3	0 vendors supporting, 0 partly or planned
Top-100 adoption	1 / 3	1% of measured sites
Spec maturity	3 / 3	Published standard

8 or more points is Established, 5 to 7 is Gaining traction, 2 to 4 is Speculative and under 2 is Stalled. A feature is also Stalled when more vendors have said no than yes. Read the spec.

Community insights

No community insights for this feature yet.

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