rexl2018/lsp-mcp

LSP MCP

A VS Code extension that provides a Language Server Protocol (LSP) MCP server, enabling AI assistants to interact with your VS Code environment for language intelligence, debugging, and code execution.

Features

• Language Intelligence: Access VS Code's language server features including:

  • Go to definition
  • Find references
  • Diagnostics (errors and warnings)
  • Symbol search
  • Call hierarchy

• Debugging Support: Control VS Code's debugger programmatically:

  • Start/stop debug sessions
  • Set and manage breakpoints
  • Step through code (into/over/out)
  • Inspect variables and call stacks
  • Evaluate expressions in debug context

Installation

Alpha Testing

Step 1: Install VS Code Extension

Download the .vsix file from Releases and install:

• In VS Code: Extensions → ... menu → Install from VSIX
• Or via command line: code --install-extension lsp-mcp-*.vsix

Step 2: Configure Claude Desktop

The MCP server connects directly to VS Code via SSE. We provide a simple stdio bridge for easy configuration.

Multi-Instance Isolation

Important: To prevent cross-workspace connections when running multiple VS Code instances, you must specify the workspace path in your Claude Desktop configuration.

Configuration

Edit your Claude Desktop configuration file:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "vscode": {
      "command": "node",
      "args": ["/path/to/lsp-mcp/bin/mcp-stdio-bridge.js", "--workspace", "/path/to/your/workspace"]
    }
  }
}

Configuration Notes:

• Replace /path/to/lsp-mcp with the actual path to this extension directory
• Replace /path/to/your/workspace with the absolute path to your VS Code workspace
• Each VS Code workspace should have its own Claude Desktop configuration with the correct workspace path
• The --workspace parameter ensures the bridge only connects to the MCP server for that specific workspace

Alternative: Auto-Discovery (Not Recommended for Multi-Instance)

For single-instance usage, you can use auto-discovery:

{
  "mcpServers": {
    "vscode": {
      "command": "node",
      "args": ["/path/to/lsp-mcp/bin/mcp-stdio-bridge.js", "--auto-discover"]
    }
  }
}

Warning: Auto-discovery may connect to any available MCP server and should not be used when running multiple VS Code instances.

VS Code Extension Configuration (Alternative)

If you're using this extension within VS Code itself, you can create a workspace-specific configuration using VS Code variables:

Create a .vscode/settings.json file in your workspace:

{
  "claude.mcpServers": {
    "vscode": {
      "command": "node",
      "args": ["/path/to/lsp-mcp/bin/mcp-stdio-bridge.js", "--workspace", "${workspaceFolder}"]
    }
  }
}

Benefits of this approach:

• Automatically uses the current workspace folder path
• No need to manually specify workspace paths
• Each VS Code workspace gets its own isolated configuration
• Works seamlessly with VS Code's variable substitution

Note: Replace /path/to/lsp-mcp with the actual path to this extension directory.

Manual Port Configuration

If you need to specify a custom port:

{
  "mcpServers": {
    "vscode": {
      "command": "node",
      "args": ["/path/to/lsp-mcp/bin/mcp-stdio-bridge.js", "--port", "8008", "--host", "localhost"]
    }
  }
}

Step 3: Restart Claude Desktop

That's it! The VS Code tools are now available in Claude.

Configure Claude Code (CLI)

For Claude Code users, use auto-discovery (recommended):

claude mcp add-json vscode '{"type":"stdio","command":"node","args":["/path/to/lsp-mcp/bin/mcp-stdio-bridge.js","--auto-discover"]}' -s user

Note: Replace /path/to/lsp-mcp with the actual path to this extension directory.

For workspace-specific connection:

claude mcp add-json vscode '{"type":"stdio","command":"node","args":["/path/to/lsp-mcp/bin/mcp-stdio-bridge.js","--workspace","/path/to/your/workspace"]}' -s user

For custom host/port settings:

claude mcp add-json vscode '{"type":"stdio","command":"node","args":["/path/to/lsp-mcp/bin/mcp-stdio-bridge.js","--port","8008","--host","localhost"]}' -s user

Multi-Instance Support

This extension supports running multiple VS Code instances simultaneously, with each instance automatically getting its own unique port. This ensures that clients can connect to the correct server without conflicts.

How It Works

1. Automatic Port Assignment: Each VS Code instance automatically gets assigned a unique port (starting from 8008)
2. Workspace Discovery: The extension creates discovery files that help clients find the right server
3. Client Auto-Discovery: The stdio bridge can automatically discover and connect to the appropriate server

Discovery Mechanisms

The stdio bridge uses multiple methods to find the correct MCP server:

1. Workspace Discovery File: Each workspace creates a .vscode/mcp-server.json file with server information
2. Global Port Registry: A system-wide registry tracks all active MCP servers
3. Port Scanning: As a fallback, the bridge scans common ports to find available servers

Best Practices

• Use --auto-discover for automatic server detection
• Use --workspace /path/to/workspace to connect to a specific workspace
• The extension handles port conflicts automatically - no manual configuration needed

Usage

Once installed, the extension shows the MCP server status in the VS Code status bar (bottom right).

To start the MCP server: Click on "LSP MCP: Stopped" in the status bar. It will change to "LSP MCP: Running (Port: XXXX)" when active.

The status bar indicates:

• LSP MCP: Running (Port: XXXX) - Server is running on the specified port and ready for connections
• LSP MCP: Stopped - Server is not running

Click the status bar item to toggle the server on/off.

How It Works

┌─────────────┐     HTTP/SSE     ┌─────────────┐
│   Claude    │ ◄──────────────► │   VS Code   │
│   Desktop   │    :8008/mcp     │  Extension  │
└─────────────┘                  └─────────────┘

1. VS Code Extension provides an SSE (Server-Sent Events) endpoint at localhost:8008/mcp
2. Claude Desktop connects directly to the VS Code extension via HTTP/SSE
3. Real-time communication enables immediate access to VS Code's language server features

Troubleshooting

If Claude can't connect to VS Code:

1. Check VS Code is running with the extension active
2. Check the status bar shows "LSP MCP: Running"
3. Test the SSE endpoint: Open http://localhost:8008/mcp in your browser to verify the connection
4. Check firewall isn't blocking localhost:8008
5. Try manually starting the MCP server in VS Code (Cmd/Ctrl+Shift+P → "Start MCP Server")
6. Restart Claude Desktop after making configuration changes

Available Tools

The extension provides 26 tools organized into three main categories:

Language Intelligence Tools (8 tools)

Refactoring Tools (1 tool)

Debug Tools (17 tools)

Breakpoint Management

Session Management

Runtime Control

Inspection and Evaluation

Tool Features

All tools support:

• Compact format - Optimized for AI token efficiency
• Detailed format - Full data for complex analysis
• Symbol-based navigation - Work with names instead of file/line numbers
• Workspace-wide operations - Not limited to single files
• Language server integration - Accurate semantic understanding

Usage Examples for AI Assistants

When connected via MCP, AI assistants can use these tools to help users with development tasks:

Finding and Understanding Code

User: "What does the handleRequest function do?"
AI uses: hover({ symbol: "handleRequest" })
→ Gets type signature and documentation without reading entire files

User: "Where is the DatabaseConnection class defined?"
AI uses: definition({ symbol: "DatabaseConnection" })
→ Instantly finds the file and line where it's declared

User: "Show me all places where processPayment is called"
AI uses: callHierarchy({ symbol: "processPayment", direction: "incoming" })
→ Gets complete list of callers with their locations

User: "Generate a visual call tree for the entire authentication flow"
AI uses: hierarchyTree({ symbol: "authenticate", direction: "outgoing", depth: 5, includeDetails: true })
→ Creates a multi-level call hierarchy with Mermaid diagram showing the complete authentication flow

Refactoring

User: "Rename the oldMethodName method to newMethodName everywhere"
AI uses: refactor_rename({ symbol: "oldMethodName", newName: "newMethodName" })
→ Safely renames across all files, updating imports and references

Debugging

User: "Help me debug why the server crashes"
AI uses: debug_listConfigurations({})
→ Shows available debug configurations

AI uses: debug_startSession({ configuration: "Debug Server" })
→ Starts the debug session

User: "Set a breakpoint where errors are handled"
AI uses: debug_setBreakpoint({ symbol: "handleError" })
→ Sets breakpoint on the function

User: "What's the value of the user object here?"
AI uses: debug_inspectVariables({ scope: "locals", filter: "user" })
→ Shows current value of user variable in debug context

User: "Why is this condition true?"
AI uses: debug_evaluateExpression({ expression: "users.length > 0 && isActive" })
→ Evaluates the expression in current debug scope

Development

Building from Source

# Clone the repository
git clone https://github.com/rexl2018/lsp-mcp.git
cd lsp-mcp

# Install dependencies
npm install

# Build the VS Code extension
npm run compile

# Package the VS Code extension
npx vsce package

Testing Local Changes

To test your local development version:

1. VS Code Extension: Press F5 in VS Code to launch Extension Development Host
2. MCP Connection: The development extension will run on the same SSE endpoint (localhost:8008/mcp)
3. Claude Configuration: No changes needed to Claude config - it will automatically connect to the development instance

Reference

Most of the code is based on the mcp-server-vscode project.

License

This project is licensed under the MIT License - see the file for details.