Use This MCP server To

Enable go-to-definition in codebases for MCP clients Provide symbol references lookup for code navigation Support rename refactoring across project files Expose real-time diagnostics and error reporting Integrate semantic code tools into AI-assisted IDEs Enhance LLMs with language server protocol features

README

MCP Language Server

This is an MCP server that runs and exposes a language server to LLMs. Not a language server for MCP, whatever that would be.

Demo

mcp-language-server helps MCP enabled clients navigate codebases more easily by giving them access semantic tools like get definition, references, rename, and diagnostics.

Setup

Install Go: Follow instructions at https://golang.org/doc/install
Install or update this server: go install github.com/isaacphi/mcp-language-server@latest
Install a language server: follow one of the guides below
Configure your MCP client: follow one of the guides below

Go (gopls)

Install gopls: go install golang.org/x/tools/gopls@latest

Configure your MCP client: This will be different but similar for each client. For Claude Desktop, add the following to ~/Library/Application\ Support/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "language-server": {
      "command": "mcp-language-server",
      "args": ["--workspace", "/Users/you/dev/yourproject/", "--lsp", "gopls"],
      "env": {
        "PATH": "/opt/homebrew/bin:/Users/you/go/bin",
        "GOPATH": "/users/you/go",
        "GOCACHE": "/users/you/Library/Caches/go-build",
        "GOMODCACHE": "/Users/you/go/pkg/mod"
      }
    }
  }
}

Note: Not all clients will need these environment variables. For Claude Desktop you will need to update the environment variables above based on your machine and username:

PATH needs to contain the path to go and to gopls. Get this with echo $(which go):$(which gopls)
GOPATH, GOCACHE, and GOMODCACHE may be different on your machine. These are the defaults.

Rust (rust-analyzer)

Install rust-analyzer: rustup component add rust-analyzer

Configure your MCP client: This will be different but similar for each client. For Claude Desktop, add the following to ~/Library/Application\ Support/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "language-server": {
      "command": "mcp-language-server",
      "args": [
        "--workspace",
        "/Users/you/dev/yourproject/",
        "--lsp",
        "rust-analyzer"
      ]
    }
  }
}

Python (pyright)

Install pyright: npm install -g pyright

Configure your MCP client: This will be different but similar for each client. For Claude Desktop, add the following to ~/Library/Application\ Support/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "language-server": {
      "command": "mcp-language-server",
      "args": [
        "--workspace",
        "/Users/you/dev/yourproject/",
        "--lsp",
        "pyright-langserver",
        "--",
        "--stdio"
      ]
    }
  }
}

Typescript (typescript-language-server)

Install typescript-language-server: npm install -g typescript typescript-language-server

Configure your MCP client: This will be different but similar for each client. For Claude Desktop, add the following to ~/Library/Application\ Support/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "language-server": {
      "command": "mcp-language-server",
      "args": [
        "--workspace",
        "/Users/you/dev/yourproject/",
        "--lsp",
        "typescript-language-server",
        "--",
        "--stdio"
      ]
    }
  }
}

C/C++ (clangd)

Install clangd: Download prebuilt binaries from the official LLVM releases page or install via your system's package manager (e.g., apt install clangd, brew install clangd).

Configure your MCP client: This will be different but similar for each client. For Claude Desktop, add the following to ~/Library/Application\\ Support/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "language-server": {
      "command": "mcp-language-server",
      "args": [
        "--workspace",
        "/Users/you/dev/yourproject/",
        "--lsp",
        "/path/to/your/clangd_binary",
        "--",
        "--compile-commands-dir=/path/to/yourproject/build_or_compile_commands_dir"
      ]
    }
  }
}

<p><strong>Note</strong>:</p>
<ul>
  <li>Replace <code>/path/to/your/clangd_binary</code> with the actual path to your clangd executable.</li>
  <li><code>--compile-commands-dir</code> should point to the directory containing your <code>compile_commands.json</code> file (e.g., <code>./build</code>, <code>./cmake-build-debug</code>).</li>
  <li>Ensure <code>compile_commands.json</code> is generated for your project for clangd to work effectively.</li>
</ul>

Other

I have only tested this repo with the servers above but it should be compatible with many more. Note:

The language server must communicate over stdio.
Any aruments after -- are sent as arguments to the language server.
Any env variables are passed on to the language server.

Tools

definition: Retrieves the complete source code definition of any symbol (function, type, constant, etc.) from your codebase.
references: Locates all usages and references of a symbol throughout the codebase.
diagnostics: Provides diagnostic information for a specific file, including warnings and errors.
hover: Display documentation, type hints, or other hover information for a given location.
rename_symbol: Rename a symbol across a project.
edit_file: Allows making multiple text edits to a file based on line numbers. Provides a more reliable and context-economical way to edit files compared to search and replace based edit tools.

About

This codebase makes use of edited code from gopls to handle LSP communication. See ATTRIBUTION for details. Everything here is covered by a permissive BSD style license.

mcp-go is used for MCP communication. Thank you for your service.

This is beta software. Please let me know by creating an issue if you run into any problems or have suggestions of any kind.

Contributing

Please keep PRs small and open Issues first for anything substantial. AI slop O.K. as long as it is tested, passes checks, and doesn't smell too bad.

Setup

Clone the repo:

git clone https://github.com/isaacphi/mcp-language-server.git
cd mcp-language-server

A justfile is included for convenience:

just -l
Available recipes:
    build    # Build
    check    # Run code audit checks
    fmt      # Format code
    generate # Generate LSP types and methods
    help     # Help
    install  # Install locally
    snapshot # Update snapshot tests
    test     # Run tests

Configure your Claude Desktop (or similar) to use the local binary:

{
  "mcpServers": {
    "language-server": {
      "command": "/full/path/to/your/clone/mcp-language-server/mcp-language-server",
      "args": [
        "--workspace",
        "/path/to/workspace",
        "--lsp",
        "language-server-executable"
      ],
      "env": {
        "LOG_LEVEL": "DEBUG"
      }
    }
  }
}

Rebuild after making changes.

Logging

Setting the LOG_LEVEL environment variable to DEBUG enables verbose logging to stderr for all components including messages to and from the language server and the language server's logs.

LSP interaction

internal/lsp/methods.go contains generated code to make calls to the connected language server.
internal/protocol/tsprotocol.go contains generated code for LSP types. I borrowed this from gopls's source code. Thank you for your service.
LSP allows language servers to return different types for the same methods. Go doesn't like this so there are some ugly workarounds in internal/protocol/interfaces.go.

Local Development and Snapshot Tests

There is a snapshot test suite that makes it a lot easier to try out changes to tools. These run actual language servers on mock workspaces and capture output and logs.

You will need the language servers installed locally to run them. There are tests for go, rust, python, and typescript.

integrationtests/
├── tests/        # Tests are in this folder
├── snapshots/    # Snapshots of tool outputs
├── test-output/  # Gitignored folder showing the final state of each workspace and logs after each test run
└── workspaces/   # Mock workspaces that the tools run on

To update snapshots, run UPDATE_SNAPSHOTS=true go test ./integrationtests/...

mcp-language-server FAQ

How do I integrate mcp-language-server with my MCP client?

You connect your MCP client to the mcp-language-server endpoint, which exposes language server protocol features over MCP, enabling semantic code operations.

Does mcp-language-server support all programming languages?

It supports languages for which language servers are available and configured, as it acts as a bridge to existing language servers.

Can mcp-language-server provide real-time diagnostics?

Yes, it exposes diagnostics from the underlying language server to MCP clients for immediate error and warning feedback.

Is mcp-language-server compatible with multiple LLM providers?

Yes, it works with MCP clients using models like OpenAI, Anthropic Claude, and Google Gemini by providing standardized semantic tooling.

What protocols does mcp-language-server use to communicate?

It uses the Language Server Protocol (LSP) adapted to MCP for communication between the server and MCP clients.

How does mcp-language-server improve AI-assisted code editing?

By providing semantic context like definitions and references, it enables LLMs to understand and manipulate code more accurately.

Is mcp-language-server open source and actively maintained?

Yes, it is open source with active CI workflows and Go module support, ensuring reliability and ongoing improvements.

Can mcp-language-server handle rename refactoring safely?

Yes, it leverages language server capabilities to perform safe and consistent renaming across the codebase.