Protocol Overview

MDP is a discovery protocol and an RPC bridge protocol.

The client provides path descriptors. The server stores and indexes them. The MCP host consumes them through a fixed bridge surface.

The wire model is transport-agnostic. The current implementation ships with:

• ws / wss sessions
• http / https loop sessions
• explicit updateClientCatalog lifecycle messages for replacing the registered path catalog after registration
• optional auth envelopes on registerClient and callClient
• transport auth from request headers or /mdp/auth cookie bootstrap
• GET /mdp/meta as an out-of-band probe for MDP server discovery

The current server implementation can also run in a layered topology:

• a standalone hub that owns the MCP bridge
• an edge server that accepts local client sessions
• optional upstream proxying from edge to hub

That discovery and proxy behavior is transport control-plane behavior. It does not add new MDP wire messages.

MDP path node categories:

• endpoint
• prompt
• skill

Endpoint nodes use an HTTP-like shape with a concrete method plus a path pattern such as GET /goods/:id. Prompt nodes use reserved leaf names that end with /prompt.md. Skill nodes use reserved leaf names that end with /skill.md, which works well for hierarchical Markdown documents such as /topic/skill.md and /topic/detail/skill.md.

The path model is the API surface. Clients register descriptors directly as endpoint, prompt, and skill paths, and hosts consume them through the canonical path-oriented bridge.