API Catalog is an IETF standard (RFC 9727) that defines a well-known location for declaring the public APIs a site exposes. Sites publish /.well-known/api-catalog with structured links to API documentation, OpenAPI specs and machine-readable endpoint information.
Agents that want to call a site's APIs need to find them. Hard-coding URLs is fragile. API Catalog provides a standard discovery path so agents can dynamically discover and call APIs.
Links to OpenAPI specs, GraphQL schemas, RPC manifests. Authentication requirements (often references to OAuth Discovery and OAuth Protected Resource). Versioning information.
Publish /.well-known/api-catalog with the standard JSON structure. The Spacemen Digital AI Agent Readiness Check tests for API Catalog presence.
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