Protocol Reference

From the server's point of view, MDP is a small set of lifecycle and routing messages.

Core flow

The main sequence is:

1. a client connects over ws / wss or http / https loop mode
2. the client sends registerClient with path catalog metadata
3. the server indexes that catalog in memory
4. an MCP host calls a bridge tool
5. the server routes the request as callClient
6. the client returns callClientResult

In an optional layered deployment, one edge server may mirror its locally connected clients into one upstream hub. That does not change the client-facing message set. The edge server still receives normal registerClient and callClientResult traffic from its clients and emits normal registrations and invocations toward the upstream hub.

What the server cares about

The server runtime only needs a few protocol concepts:

• client descriptors
• path descriptors for endpoints, prompts, and skills
• invocation envelopes with optional auth
• heartbeat messages for connection liveness

The transport-facing control plane also includes an HTTP metadata probe at /mdp/meta. That probe helps one server decide whether another local port is already serving MDP and whether it should proxy upward instead of acting as the root hub.

Read deeper

The detailed protocol pages remain the source of truth:

• Overview
• Capability Model
• Progressive Disclosure
• Transport
• Lifecycle
• Message Schema