MCP Language Server

What isaacphi/mcp-language-server MCP server does

The isaacphi/mcp-language-server MCP server exposes a language server to MCP-enabled clients. It is intended for navigating and modifying source code with semantic information supplied by an underlying Language Server Protocol implementation.

The server works against a configured workspace. Instead of asking an agent to infer relationships from file text alone, it provides operations based on symbols, source locations, references, diagnostics, and language-server responses. It is useful for repositories where an installed language server can understand the project and its dependencies.

How it works

The MCP process launches a language-server executable and communicates with it over standard input and output. The language-server program must support stdio communication. The --workspace option selects the codebase, while --lsp identifies the executable or path to launch. Arguments after -- are forwarded to that language server, and configured environment variables are passed through to it.

The project has documented configurations for Go with gopls, Rust with rust-analyzer, Python with pyright-langserver, TypeScript with typescript-language-server, and C or C++ with clangd. Other language servers may work when they meet the stdio requirement, but the README states that only the listed servers were tested.

Setup and configuration

Install Go first, then install the server with:

go install github.com/isaacphi/mcp-language-server@latest

Install the language server for the language used by the target workspace. For example, the documented commands include go install golang.org/x/tools/gopls@latest, rustup component add rust-analyzer, and global npm installation for Pyright or TypeScript language-server packages.

An MCP client configuration needs the mcp-language-server command and arguments resembling --workspace, a real workspace path, --lsp, and the language-server command. Claude Desktop is the example client shown in the documentation. C or C++ projects may also need clangd's --compile-commands-dir option pointing to a directory containing compile_commands.json.

Tools and capabilities

The isaacphi/mcp-language-server MCP server provides these MCP tools:

• definition returns the complete source definition for a symbol such as a function, type, or constant.
• references finds usages of a symbol across the workspace.
• diagnostics reports warnings and errors for a specified file.
• hover returns documentation, type information, or other hover data for a location.
• rename_symbol renames a symbol across a project.
• edit_file applies multiple text edits to a file using line numbers, offering an alternative to search-and-replace editing.

Limitations and notes

This project is described as beta software. Its results depend on the selected language server and that server's project configuration. The underlying executable must communicate over stdio, and language-specific setup may be required before semantic features work correctly. For clangd, the documentation specifically notes that an appropriate compile_commands.json should be generated.

The README identifies edited code from gopls for LSP communication and says the codebase is covered by a permissive BSD-style license. It also documents LOG_LEVEL=DEBUG for verbose logging to standard error during development or troubleshooting.