Well-known URI

Discover A well-known URI is a path beginning /.well-known/ at the root of an origin, reserved by RFC 8615 (May 2019, obsoleting RFC 5785) so that applications needing site-wide metadata do not have to negotiate arbitrary paths or risk colliding with a site's existing URL space. Anyone minting a new well-known name is expected to register it with IANA, referencing the specification that defines its format and media type; the mechanism itself defines no content at /.well-known/ and clients should not assume anything exists there by default. The agentic web reuses this pattern heavily: /.well-known/agent-card.json (A2A), /.well-known/ard.json and its predecessor /.well-known/ai-catalog.json (ARD), and others each register or informally claim a name under this prefix rather than inventing a new discovery convention. Used by: a2a, ard, ai-catalog-well-known-file.