debugmcpdev/mcp-debugger

mcp-debugger

MCP server for step-through debugging – give your AI agents debugging superpowers 🚀

🎯 Overview

mcp-debugger is a Model Context Protocol (MCP) server that provides debugging tools as structured API calls. It enables AI agents to perform step-through debugging of Python scripts using the Debug Adapter Protocol (DAP).

🎬 Demo Video: See the debugger in action!

Recording in progress - This will show an AI agent discovering and fixing the variable swap bug in real-time

✨ Key Features

• 🐍 Python debugging via debugpy – Full DAP protocol support
• 🔄 STDIO and SSE transport modes – Works with any MCP client
• 🧪 >90% test coverage – Battle-tested with 657+ passing tests
• 🐳 Docker and npm packages – Deploy anywhere
• 🤖 Built for AI agents – Structured JSON responses for easy parsing

🚀 Quick Start

For MCP Clients (Claude Desktop, etc.)

Add to your MCP settings configuration:

{
  "mcpServers": {
    "mcp-debugger": {
      "command": "node",
      "args": ["C:/path/to/mcp-debugger/dist/index.js", "--log-level", "debug", "--log-file", "C:/path/to/logs/debug-mcp-server.log"],
      "disabled": false,
      "autoApprove": ["create_debug_session", "set_breakpoint", "get_variables"]
    }
  }
}

Using Docker

docker run -v $(pwd):/workspace debugmcp/mcp-debugger:0.9.0

Using npm

npm install -g mcp-debugger
mcp-debugger --help

📸 Screenshot: MCP Integration in Action

This screenshot will show real-time MCP protocol communication with tool calls and JSON responses flowing between the AI agent and debugger.

📚 How It Works

mcp-debugger exposes debugging operations as MCP tools that can be called with structured JSON parameters:

// Tool: create_debug_session
// Request:
{
  "language": "python",
  "name": "My Debug Session"
}
// Response:
{
  "success": true,
  "sessionId": "a4d1acc8-84a8-44fe-a13e-28628c5b33c7",
  "message": "Created python debug session: My Debug Session"
}

📸 Screenshot: Active Debugging Session

This screenshot will show the debugger paused at a breakpoint with the stack trace visible in the left panel, local variables in the right panel, and source code with line highlighting in the center.

🛠️ Available Tools

📸 Screenshot: Multi-Session Debugging

This screenshot will show the debugger managing multiple concurrent debug sessions, demonstrating how AI agents can debug different scripts simultaneously with isolated session management.

💡 Example: Debugging Python Code

Here's a complete debugging session example:

# buggy_swap.py
def swap_variables(a, b):
    a = b  # Bug: loses original value of 'a'
    b = a  # Bug: 'b' gets the new value of 'a'
    return a, b

Step 1: Create a Debug Session

// Tool: create_debug_session
// Request:
{
  "language": "python",
  "name": "Swap Bug Investigation"
}
// Response:
{
  "success": true,
  "sessionId": "a4d1acc8-84a8-44fe-a13e-28628c5b33c7",
  "message": "Created python debug session: Swap Bug Investigation"
}

Step 2: Set Breakpoints

// Tool: set_breakpoint
// Request:
{
  "sessionId": "a4d1acc8-84a8-44fe-a13e-28628c5b33c7",
  "file": "buggy_swap.py",
  "line": 2
}
// Response:
{
  "success": true,
  "breakpointId": "28e06119-619e-43c0-b029-339cec2615df",
  "file": "C:\\path\\to\\buggy_swap.py",
  "line": 2,
  "verified": false,
  "message": "Breakpoint set at C:\\path\\to\\buggy_swap.py:2"
}

Step 3: Start Debugging

// Tool: start_debugging
// Request:
{
  "sessionId": "a4d1acc8-84a8-44fe-a13e-28628c5b33c7",
  "scriptPath": "buggy_swap.py"
}
// Response:
{
  "success": true,
  "state": "paused",
  "message": "Debugging started for buggy_swap.py. Current state: paused",
  "data": {
    "message": "Debugging started for buggy_swap.py. Current state: paused",
    "reason": "breakpoint"
  }
}

Step 4: Inspect Variables

First, get the scopes:

// Tool: get_scopes
// Request:
{
  "sessionId": "a4d1acc8-84a8-44fe-a13e-28628c5b33c7",
  "frameId": 3
}
// Response:
{
  "success": true,
  "scopes": [
    {
      "name": "Locals",
      "variablesReference": 5,
      "expensive": false,
      "presentationHint": "locals",
      "source": {}
    },
    {
      "name": "Globals", 
      "variablesReference": 6,
      "expensive": false,
      "source": {}
    }
  ]
}

Then get the local variables:

// Tool: get_variables
// Request:
{
  "sessionId": "a4d1acc8-84a8-44fe-a13e-28628c5b33c7",
  "scope": 5
}
// Response:
{
  "success": true,
  "variables": [
    {"name": "a", "value": "10", "type": "int", "variablesReference": 0, "expandable": false},
    {"name": "b", "value": "20", "type": "int", "variablesReference": 0, "expandable": false}
  ],
  "count": 2,
  "variablesReference": 5
}

📸 Screenshot: Variable Inspection Reveals the Bug

This screenshot will show the TUI visualizer after stepping over line 4, where both variables incorrectly show value 20, clearly demonstrating the variable swap bug. The left panel shows the execution state, the center shows the highlighted code, and the right panel displays the incorrect variable values.

📖 Documentation

• 📘 – Complete API documentation
• 🚦 – First-time setup
• 🐍 – Python-specific features
• 🔧 – Common issues & solutions
• 🏗️ – Technical deep-dive

🤝 Contributing

We welcome contributions! See for guidelines.

# Development setup
git clone https://github.com/debugmcp/mcp-debugger.git
cd mcp-debugger
npm install
npm run build
npm test

Running Container Tests Locally

We use Act to run GitHub Actions workflows locally:

# Build the Docker image first
docker build -t mcp-debugger:local .

# Run tests with Act (use WSL2 on Windows)
act -j build-and-test --matrix os:ubuntu-latest

See for detailed testing instructions.

📊 Project Status

• ✅ Production Ready: v0.9.0 with comprehensive test coverage
• 🚧 Coming Soon: Expression evaluation, conditional breakpoints
• 📈 Active Development: Regular updates and improvements

See for planned features.

📄 License

MIT License - see for details.

🙏 Acknowledgments

Built with:

• Model Context Protocol by Anthropic
• Debug Adapter Protocol by Microsoft
• debugpy for Python debugging

Give your AI the power to debug like a developer! 🎯