VS Code LM Tools MCP Server Extension

A VS Code extension that creates an MCP (Model Context Protocol) server to expose VS Code Language Model tools over HTTP, enabling external applications to access and utilize VS Code's built-in LM tools.

Features

This extension provides the following functionality:

• MCP Server: Creates a Model Context Protocol server that runs on http://localhost:22333
• VS Code LM Tools Integration: Automatically discovers and exposes all registered VS Code Language Model tools
• HTTP API: Provides a REST-like interface for external applications to interact with VS Code LM tools
• Tool Discovery: Lists all available VS Code LM tools with their descriptions and input schemas
• Tool Invocation: Attempts to invoke VS Code LM tools (with limitations outside chat context)

How to Use

Starting the MCP Server

1. Install and activate the extension
2. The MCP server will automatically start on port 22333 when the extension activates
3. You'll see a notification: "MCP Server started on port 22333"

Accessing the MCP Server

The server exposes the following MCP protocol endpoints:

• Initialize: POST http://localhost:22333 with {"method": "initialize", ...}
• List Tools: POST http://localhost:22333 with {"method": "tools/list", ...}
• Call Tool: POST http://localhost:22333 with {"method": "tools/call", ...}
• Ping: POST http://localhost:22333 with {"method": "ping", ...}

Requirements

• VS Code version 1.102.0 or higher
• Node.js and npm for development
• Network access to localhost port 22333

Technical Details

MCP Protocol Implementation

The extension implements a subset of the Model Context Protocol (MCP) v2024-11-05:

• Server Info: vscode-lm-tools-mcp-server v1.0.0
• Capabilities: Supports tools discovery and invocation
• Transport: HTTP with JSON-RPC 2.0 format
• CORS: Enabled for cross-origin requests

VS Code LM Tools Integration

• Automatically discovers all registered vscode.lm.tools
• Normalizes tool input schemas to ensure MCP compatibility
• Handles tool invocation with proper error handling
• Provides detailed tool information when direct invocation fails

Limitations

• Tool invocation requires a toolInvocationToken which is only available in chat contexts
• Outside of chat contexts, the server returns tool metadata instead of execution results
• Some VS Code LM tools may not be accessible depending on the current workspace and context

Extension Settings

This extension does not currently contribute any VS Code settings.

Known Issues

• Direct tool invocation may fail outside of VS Code chat contexts due to toolInvocationToken requirements
• Tool availability depends on other installed extensions and workspace configuration
• Server runs on a fixed port (22333) which may conflict with other applications

Release Notes

0.0.1

Initial release featuring:

• MCP server implementation with HTTP transport
• VS Code LM tools discovery and exposure
• Basic tool invocation with fallback to metadata

Development

Building the Extension

npm install
npm run compile

Running Tests

npm test

Packaging

npm run package

MCP Client Usage

To connect to this MCP server from an MCP client, add the following configuration to your mcp.json file:

Streamable HTTP Transport (Recommended)

{
  "servers": {
    "vscode": {
      "type": "streamable-http",
      "url": "http://localhost:22333"
    }
  }
}

Standard HTTP Transport

{
  "servers": {
    "vscode": {
      "type": "http",
      "url": "http://localhost:22333"
    }
  }
}

Prerequisites

1. Ensure this VS Code extension is installed and active
2. The MCP server will automatically start on port 22333
3. Your MCP client should be configured to connect to the above URL

Available Operations

Once connected, your MCP client will have access to:

• Tool Discovery: Automatically list all VS Code LM tools
• Tool Invocation: Execute VS Code LM tools (with context limitations)
• Schema Information: Access input schemas for each tool

Dependencies

• @modelcontextprotocol/sdk: Core MCP SDK for server implementation
• VS Code API: For accessing Language Model tools and extension functionality

Contributing

This extension follows VS Code extension development best practices:

• Extension Guidelines
• VS Code API Documentation

License

See the LICENSE file for details.