Tritlo/lsp-mcp

An MCP (Model Context Protocol) server for interacting with LSP (Language Server Protocol) interface.
This server acts as a bridge that allows LLMs to query LSP Hover and Completion providers.
Overview
The MCP Server works by:
1. Starting an LSP client that connects to a LSP server
2. Exposing MCP tools that send requests to the LSP server
3. Returning the results in a format that LLMs can understand and use
This enables LLMs to utilize LSPs for more accurate code suggestions.
Configuration:
Features
MCP Tools
- get_info_on_location: Get hover information at a specific location in a file
- get_completions: Get completion suggestions at a specific location in a file
- get_code_actions: Get code actions for a specific range in a file
- open_document: Open a file in the LSP server for analysis
- close_document: Close a file in the LSP server
- get_diagnostics: Get diagnostic messages (errors, warnings) for open files
- start_lsp: Start the LSP server with a specified root directory
- restart_lsp_server: Restart the LSP server without restarting the MCP server
- set_log_level: Change the server's logging verbosity level at runtime
MCP Resources
- lsp-diagnostics:// resources for accessing diagnostic messages with real-time updates via subscriptions
- lsp-hover:// resources for retrieving hover information at specific file locations
- lsp-completions:// resources for getting code completion suggestions at specific positions
Additional Features
- Comprehensive logging system with multiple severity levels
- Colorized console output for better readability
- Runtime-configurable log level
- Detailed error handling and reporting
- Simple command-line interface
Prerequisites
- Node.js (v16 or later)
- npm
For the demo server:
- GHC (8.10 or later)
- Cabal (3.0 or later)
Installation
Building the MCP Server
1. Clone this repository:
2. Install dependencies:
3. Build the MCP server:
Testing
The project includes integration tests for the TypeScript LSP support. These tests verify that the LSP-MCP server correctly handles LSP operations like hover information, completions, diagnostics, and code actions.
Running Tests
To run the TypeScript LSP tests:
or specifically:
Test Coverage
The tests verify the following functionality:
- Initializing the TypeScript LSP with a mock project
- Opening TypeScript files for analysis
- Getting hover information for functions and types
- Getting code completion suggestions
- Getting diagnostic error messages
- Getting code actions for errors
The test project is located in test/ts-project/ and contains TypeScript files with intentional errors to test diagnostic feedback.
Usage
Run the MCP server by providing the path to the LSP executable and any arguments to pass to the LSP server:
For example:
Important: Starting the LSP Server
With version 0.2.0 and later, you must explicitly start the LSP server by calling the start_lsp tool before using any LSP functionality. This ensures proper initialization with the correct root directory, which is especially important when using tools like npx:
Logging
The server includes a comprehensive logging system with 8 severity levels:
- debug: Detailed information for debugging purposes
- info: General informational messages about system operation
- notice: Significant operational events
- warning: Potential issues that might need attention
- error: Error conditions that affect operation but don't halt the system
- critical: Critical conditions requiring immediate attention
- alert: System is in an unstable state
- emergency: System is unusable
By default, logs are sent to:
1. Console output with color-coding for better readability
2. MCP notifications to the client (via the notifications/message method)
Viewing Debug Logs
For detailed debugging, you can:
1. Use the claude --mcp-debug flag when running Claude to see all MCP traffic between Claude and the server: