debug-mcp-server

A minimal Model Context Protocol server for debugging MCP clients. It echoes back everything it receives — tool arguments, session IDs, metadata — so you can inspect exactly what your client is sending.

Uses Streamable HTTP transport (no stdio).

Tools

Tool	Description
debug_echo	Returns all passed arguments as JSON along with sessionId and _meta
debug_inspect	Recursively prints the type and structure of any value
debug_server_info	Returns Node.js version, platform, uptime, memory usage

Requirements

• Node.js 18+

Installation

git clone https://github.com/your-username/debug-mcp-server.git
cd debug-mcp-server
npm install

Usage

npm start
# Server listening on http://127.0.0.1:3000/mcp

Environment variables:

Variable	Default	Description
PORT	3000	Port to listen on
HOST	127.0.0.1	Host to bind to

Connect to Claude Code

claude mcp add --transport http debug-mcp-server http://127.0.0.1:3000/mcp

API

All requests go to POST /mcp. The session lifecycle follows the MCP Streamable HTTP spec:

1. Initialize — send an initialize request without mcp-session-id; the server responds with the header mcp-session-id
2. Subsequent requests — include mcp-session-id in every request
3. SSE stream — GET /mcp with mcp-session-id opens a server-sent events stream for server→client notifications
4. Terminate — DELETE /mcp with mcp-session-id closes the session

Every incoming request (headers + body) is logged to stdout.

Example session

# 1. Initialize
curl -sD - -X POST http://127.0.0.1:3000/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{
    "jsonrpc": "2.0", "id": 1, "method": "initialize",
    "params": {
      "protocolVersion": "2024-11-05",
      "capabilities": {},
      "clientInfo": { "name": "test", "version": "1.0" }
    }
  }'
# → header: mcp-session-id: <SESSION_ID>

# 2. Call debug_echo
curl -s -X POST http://127.0.0.1:3000/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -H "mcp-session-id: <SESSION_ID>" \
  -d '{
    "jsonrpc": "2.0", "id": 2, "method": "tools/call",
    "params": {
      "name": "debug_echo",
      "arguments": { "message": "hello", "number": 42, "flag": true }
    }
  }'

Response from debug_echo:

{
  "tool": "debug_echo",
  "timestamp": "2026-06-23T10:56:52.842Z",
  "params": {
    "message": "hello",
    "number": 42,
    "flag": true
  },
  "meta": null,
  "sessionId": "<SESSION_ID>"
}

License

MIT