Protected Resource Metadata (PRM) standardizes how APIs, as resource servers, advertise their access requirements within the OAuth framework, enhancing security and interoperability by enabling OAuth clients to discover authorization requirements automatically through a machine-readable JSON document hosted at a well-known URL. This is crucial in today's dynamic technological landscape, characterized by AI agents, microservices, and the Model Context Protocol (MCP), which require real-time, secure API integrations without hard-coded configurations. By completing the trio of OAuth metadata standards alongside Dynamic Client Registration and Authorization Server Metadata, PRM allows APIs to specify trusted authorization servers, expected scopes, token formats, and special security requirements, facilitating more dynamic and autonomous operations. This advancement supports progressive scoping, where clients request only the necessary OAuth scopes for specific operations, and introduces features like JWT-signed metadata and dynamic updates through HTTP 401 responses, ensuring APIs become self-describing, adaptable, and part of a federated internet. Implementing PRM requires best practices like serving metadata over HTTPS and verifying JWT signatures to enhance API security effectively, making it a crucial component for modern API development and the agent-driven, zero-trust environments of the future.