The "mcp" URI Scheme and MCP Server Discovery Mechanism

The Model Context Protocol (MCP) defines a standard interface for AI agents to connect to external tools and services. However, no standard mechanism exists for an AI agent to autonomously discover which web domains expose an MCP server. This document defines: (1) the "mcp" URI scheme, a machine-to-machine identifier for publicly reachable MCP servers; (2) a two-mode discovery mechanism: a well-known URI (/.well-known/mcp-server) for universal compatibility, and a DNS TXT record format for DNS-native fast discovery; (3) an optional manifest integrity mechanism using JSON Web Signatures (JWS, [RFC7515]) with keys published via DNS; (4) a security capability negotiation mechanism through which the manifest declares trust class, authentication requirements, compliance frameworks, and logging policy before connection. This specification does not define the MCP protocol itself, nor authentication between agent and server. Those are covered by the MCP specification and OAuth 2.1 respectively.