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MCP Debugger Tools

by davidfirst
  • Apple
  • Linux

MCP Debugger Tools

VSCode extension that exposes debugging capabilities via Model Context Protocol (MCP), enabling AI agents to programmatically control VSCode's debugger.

Features

The extension provides the following 4 MCP tools:

  1. add_breakpoint - Add a breakpoint to a specific file and line number
  2. remove_breakpoint - Remove a breakpoint from a specific file and line number
  3. start_debugging - Start debugging with a specific configuration
  4. stop_debugging - Stop the current debugging session

Installation & Setup

  1. Clone and build the extension:
    git clone <repository-url> cd vscode-mcp-debugger npm install npm run compile
  2. Install the extension in VSCode:
    • Press F5 to run in Extension Development Host, or
    • Package as VSIX: vsce package and install manually
  3. Verify the MCP server is available:
    • Open VSCode Command Palette (Cmd+Shift+P)
    • Run "MCP: List Servers"
    • You should see "MCP Debugger Tools" listed
  4. Enable in AI Chat:
    • Open AI Chat in VSCode
    • Click the tools icon or type / to see available tools
    • You should see the 4 debugging tools available

Usage with AI Agents

Once installed, AI agents can use these tools to:

  • Set breakpoints in your code at specific lines
  • Start debugging sessions using your launch configurations
  • Remove breakpoints when no longer needed
  • Stop debugging to clean up resources

Communication Architecture

The extension uses a unique architecture to bridge the MCP protocol with VSCode's debugging APIs:

AI Agent → MCP Server → Temp File IPC → VSCode Extension → VSCode Debug API ↑ ↓ JSON Response ← Response File ← Debug API Result

How it works:

  1. AI Agent calls MCP tools (add_breakpoint, start_debugging, etc.)
  2. MCP Server (standalone Node.js process) receives the tool calls
  3. File-based IPC - Server writes command requests to temporary files
  4. VSCode Extension monitors temp directory and processes commands
  5. VSCode Debug API - Extension uses native VSCode debugging capabilities
  6. Response cycle - Results flow back through the same IPC mechanism

This architecture ensures the MCP server runs independently while having full access to VSCode's debugging features.

Example AI Agent Workflow

AI: I'll help you debug the issue in your calculator function. 1. First, let me add a breakpoint at the start of the function: [Uses add_breakpoint tool with filePath and lineNumber] 2. Now I'll start debugging with your launch configuration: [Uses start_debugging tool] 3. After analyzing the execution, I'll clean up: [Uses remove_breakpoint and stop_debugging tools]

MCP Tools Reference

add_breakpoint

Description: Add a breakpoint to a specific file and line number

Parameters:

  • filePath (string, required): Absolute path to the file
  • lineNumber (number, required): Line number (1-based)
  • condition (string, optional): Conditional expression for the breakpoint

Example:

{ "filePath": "/path/to/your/file.js", "lineNumber": 25, "condition": "x > 10" }

remove_breakpoint

Description: Remove a breakpoint from a specific file and line number

Parameters:

  • filePath (string, required): Absolute path to the file
  • lineNumber (number, required): Line number (1-based)

Example:

{ "filePath": "/path/to/your/file.js", "lineNumber": 25 }

start_debugging

Description: Start debugging with a specific configuration

Parameters:

  • configurationName (string, optional): Name of the debug configuration to use
  • workspaceFolderPath (string, optional): Path to the workspace folder

Example:

{ "configurationName": "Launch Node.js Program", "workspaceFolderPath": "/path/to/workspace" }

stop_debugging

Description: Stop the current debugging session

Parameters:

  • sessionId (string, optional): Optional session ID to stop a specific session

Example:

{ "sessionId": "debug-session-123" }

Requirements

  • VSCode with MCP support (latest version recommended)
  • Node.js (v18+ for running the MCP server)
  • Project workspace with debug configurations in .vscode/launch.json
  • Extension Development Host (for development/testing)

Supported Platforms

  • macOS - Fully tested and supported
  • Linux - Compatible with file-based IPC
  • Windows - Should work with standard temp directory
  • ⚠️ WSL - May require additional configuration for file permissions

Debug Configuration Setup

Create a .vscode/launch.json file in your project:

{ "version": "0.2.0", "configurations": [ { "name": "Launch Node.js Program", "type": "node", "request": "launch", "program": "${workspaceFolder}/src/index.js", "console": "integratedTerminal" } ] }

Development

Building from Source

  • Install dependencies: npm install
  • Compile TypeScript: npm run compile
  • Watch for changes: npm run watch for automatic compilation
  • Testing: Use the Extension Development Host (F5)
  • Debugging: Set breakpoints in the extension code itself

Project Structure

src/ ├── extension.ts # Main extension entry point & MCP registration ├── debugBridge.ts # VSCode Debug API wrapper ├── mcpServer.ts # Standalone MCP server (stdio transport) ├── integratedMcpServer.ts # Alternative integrated server implementation └── vscodeDebuggerMcp.ts # Legacy server implementation

Key Components

  • Extension.ts: Registers MCP server definition, monitors IPC files
  • DebugBridge.ts: Provides clean interface to VSCode debugging APIs
  • mcpServer.ts: Standalone MCP server that communicates via file IPC
  • IPC System: File-based communication between processes

Contributing

  1. Fork the repository
  2. Create a feature branch
  3. Make your changes
  4. Test with Extension Development Host
  5. Submit a pull request

Please ensure all tools work correctly and add appropriate error handling.

Troubleshooting

Common Issues

  1. Tools not visible:
    • Check that MCP server is running via "MCP: List Servers"
    • Verify the extension is active in Extension Development Host
    • Look for "MCP Debugger Tools" in the MCP servers list
  2. Breakpoints not working:
    • Ensure file paths are absolute and files exist
    • Check that the file is currently open or can be opened in VSCode
    • Verify the line number is valid (1-based indexing)
  3. Debug config errors:
    • Verify .vscode/launch.json exists and is valid
    • Ensure the specified configuration name exists
    • Check that the workspace folder is correctly detected
  4. IPC communication issues:
    • Check VSCode Developer Console for error messages
    • Verify temp directory permissions (the extension uses OS temp directory)
    • Look for MCP server stderr output in "MCP: List Servers" → Show Output

Debug Mode

Enable detailed logging by checking the MCP server output:

  1. Open Command Palette (Cmd+Shift+P)
  2. Run "MCP: List Servers"
  3. Select "MCP Debugger Tools"
  4. Click "Show Output" to see server logs

Technical Details

  • MCP Server Process: Runs as standalone Node.js process via stdio transport
  • Extension Process: Runs within VSCode extension host
  • IPC Mechanism: Temporary JSON files in OS temp directory
  • Response Timeout: 10 seconds (configurable in source code)
  • File Cleanup: Automatic cleanup of temporary IPC files

License

MIT

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