MCP_INTERCEPTION_SUMMARY.md

MCP Interception Summary

How Claude Code's /ide Command Works

We've successfully set up a man-in-the-middle proxy to intercept the Model Context Protocol (MCP) communication between Claude Code and VS Code.

Key Findings:

1. MCP Server: VS Code extension runs an MCP server on localhost:40145 using WebSocket protocol
2. Lock Files: Located in ~/.claude/ide/, named by PID (e.g., 367937.lock)
3. Communication: JSON-RPC messages over WebSocket connection

Current Setup:

1. Original VS Code MCP Server: Port 40145 (PID: 367937)
2. MITM WebSocket Proxy: Port 40146 (forwards to 40145)
3. Modified Lock File: ~/.claude/ide/367937.lock points to our proxy port 40146

Testing Instructions:

1. Verify proxy is running:

   netstat -tlnp | grep 40146

2. Start Claude in debug mode:

   claude --debug

3. Type the /ide command:

   > /ide
   

4. Check captured messages:

   ls -la mitm-claude/logs/mcp_websocket/

Files Created:

• mitm-websocket.py - Basic WebSocket MITM proxy
• mitm-websocket-v2.py - Enhanced proxy with better logging
• intercept-mcp-stdio.py - Stdio interceptor (for future use)
• Various test scripts for setup and monitoring

MCP Protocol Details:

The MCP uses JSON-RPC over WebSocket with messages for:

• Tool discovery and execution
• Resource access (files, git state)
• Completion suggestions
• IDE state synchronization

Next Steps:

With the proxy in place, you can now:

1. Capture all MCP messages between Claude and VS Code
2. Analyze the protocol implementation
3. Understand how /ide integrates with the IDE
4. Potentially create custom MCP servers or clients