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Agent LighthouseAgent Lighthouse

    Searches the text of every published page. The evidence sources themselves are not in this index — search all of them on the trusted sources page.

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    agent-interfaces/mcp-discovery

    MCP servers.json discovery file (obsolete)

    What it checks

    Whether the site still publishes a file at /.well-known/mcp/servers.json. Any non-HTML 200 with a body counts: the path is MCP-specific, so nothing else is expected there.

    The /.well-known/ucp commerce profile this audit used to read is not obsolete. Google Merchant reads it, and agentic-commerce/ucp-profile judges it.

    State Result
    a file served at /.well-known/mcp/servers.json, parseable or not warn, priority low
    no response, a non-200, an HTML page, or an empty body notApplicable

    Why it matters

    Mechanism: a servers list at a well-known path would let an MCP client find a site’s servers. The claim this audit tests is that no client looks there, because MCP domain discovery uses a different path.

    Evidence

    • The MCP Server Card extension says clients performing domain-level discovery “SHOULD attempt to retrieve” /.well-known/ai-catalog.json. It lists a /.well-known/mcp path only as an alternative it considered — discovery.md (verified 2026-10-18)
    • No MCP specification revision defines /.well-known/mcp/servers.json, and no MCP client documents fetching it.
    • The path is not in the IANA Well-Known URIs registry.

    Limits

    The Server Card extension is still experimental, so the discovery route may change. If a later revision names this path, the audit is re-graded.

    How it scores

    Grade: D — no specification defines the path and no client reads it. An obsolete audit carries weight 0 and never returns fail (sunset.test.ts; Audit.toCheckResult lowers a stray fail to warn). It does not move any score.

    Why obsolete, not rejected or informative: the path never had a specification or a consumer, so nothing was withdrawn from it. It is obsolete because the MCP project settled domain discovery elsewhere: the Server Card extension names /.well-known/ai-catalog.json (and ARD now /.well-known/ard.json) and lists a /.well-known/mcp path only as an alternative it considered. A successor is documented, and sites still publish the old path, so the owner is told where the server belongs instead. This is the “superseded” case in docs/evidence/policy.md.

    Example finding

    /.well-known/mcp/servers.json lists one server. The report says no client reads the path and asks for the server’s Server Card in /.well-known/ai-catalog.json.

    Sources