mclsp

mclsp

MCP server that bridges coding agents to Language Server Protocol (LSP) capabilities.

Configure one or more LSP servers, and mclsp exposes their features — go-to-definition, find references, diagnostics, rename, and more — as MCP tools. Servers start lazily on first tool use, so there's no startup cost for languages you don't touch.

Quick Start

claude mcp add lsp -- npx -y mclsp

Then create a mclsp.yaml in your project root:

servers:
  typescript:
    command: ["typescript-language-server", "--stdio"]
    filePatterns: ["**/*.ts", "**/*.tsx", "**/*.js", "**/*.jsx"]

Configuration

Each server entry supports:

Field	Required	Description
command	Yes	Command to start the LSP server (string array)
filePatterns	Yes	Glob patterns for files this server handles
initializationOptions	No	Options passed to the LSP server on initialization
rootUri	No	Override the workspace root URI
env	No	Environment variables for the LSP server process

Multiple servers can be configured for different languages:

servers:
  typescript:
    command: ["typescript-language-server", "--stdio"]
    filePatterns: ["**/*.ts", "**/*.tsx", "**/*.js", "**/*.jsx"]
  rust:
    command: ["rust-analyzer"]
    filePatterns: ["**/*.rs"]
  ruby:
    command: ["ruby-lsp"]
    filePatterns: ["**/*.rb"]

Tools

All standard LSP tools are registered and available when a matching server is configured.

Navigation: goto_definition, goto_type_definition, goto_implementation, goto_declaration, find_references

Inspection: hover, signature_help, document_symbols, workspace_symbols

Refactoring: code_actions, rename_prepare, rename

Hierarchy: call_hierarchy_incoming, call_hierarchy_outgoing, type_hierarchy

Always available: open_file, diagnostics

All position-based tools take file (relative path), line (1-indexed), and col (1-indexed).

Server Extensions

Some LSP servers support custom methods beyond the standard protocol. mclsp includes built-in extensions for:

• Ruby LSP: ruby_discover_tests, ruby_go_to_relevant_file, ruby_show_syntax_tree, ruby_dependencies
• TypeScript: ts_go_to_source_definition, ts_organize_imports

Contributing Extensions

To add extensions for a new language server, create a file in src/extensions/ (e.g. src/extensions/python.ts):

import type { ServerExtension } from "./index.js";

const extensions: ServerExtension[] = [
  {
    name: "python_my_custom_method",
    method: "custom/myMethod",
    description: "Description of what this does",
    params: "textDocument", // or "textDocumentPosition" or "custom"
  },
];

export default extensions;

Then add the import and registry entry in src/extensions/index.ts.

License

MIT