What is Well-known URI?

A well-known URI is a conventional, predictable location, always under the /.well-known/ path of a domain, where a service publishes machine-readable metadata so clients can discover configuration without it being hand-shared. The pattern is standardized so that any client knows where to look. In MCP's OAuth 2.1 authorization flow, well-known URIs are how a client bootstraps a connection to a remote server it has only a URL for. The client fetches the protected-resource metadata (/.well-known/oauth-protected-resource) to learn which authorization server guards the endpoint, then fetches that authorization server's metadata (/.well-known/oauth-authorization-server, the format defined by RFC 8414) to find the authorization endpoint, token endpoint, registration endpoint, and supported scopes. With those documents in hand the client can run the whole sign-in, including Dynamic Client Registration and PKCE, with zero manual configuration beyond the server URL. This discovery-by-convention is what makes connecting to a brand-new remote MCP server feel like just pasting a link: the well-known documents tell the client everything it needs to authenticate.