karellen-lsp-mcp

MCP Server for LSP Code Intelligence (karellen-lsp-mcp)

Overview

karellen-lsp-mcp gives LLM clients structured code intelligence via LSP (Language Server Protocol) servers. Instead of reading through entire codebases, the LLM can query definitions, references, call hierarchies, type hierarchies, hover documentation, symbols, and diagnostics — the same information a human developer gets from their IDE.

Two interfaces, one daemon:

• MCP interface (karellen-lsp-mcp): Explicit tool calls with structured responses. Requires MCP tool approval or allow-rules.
• LSP proxy interface (karellen-lsp): Native LSP server that Claude Code uses transparently — no permission prompts, no manual project registration. Auto-detects languages and routes to backend LSP servers.

Architecture

Multiple Claude sessions share a single daemon process and a single LSP server per project, avoiding duplicate server instances and redundant indexing:

Claude Code LSP           Claude MCP Session 1      Claude MCP Session 2
     │ (stdio)                  │ (stdio)                  │ (stdio)
     ▼                          ▼                          ▼
┌─────────────┐          ┌─────────────┐          ┌─────────────┐
│  LSP proxy  │          │  MCP stdio  │          │  MCP stdio  │
│  frontend   │          │  frontend   │          │  frontend   │
└──────┬──────┘          └──────┬──────┘          └──────┬──────┘
       │ (Unix socket)          │                        │
       ▼                        ▼                        ▼
┌──────────────────────────────────────────────────────────────┐
│     karellen-lsp-mcp daemon                                  │
│                                                              │
│  Project Registry (refcounted)                               │
│    project-A  refcount=3  ──► clangd                         │
│    project-B  refcount=1  ──► jdtls                          │
└──────────────────────────────────────────────────────────────┘

• Daemon: Persistent process, owns all LSP server subprocesses and the project registry. Listens on Unix domain socket. User-scoped. Auto-starts when the first frontend connects, auto-exits after idle timeout with no connections.
• MCP frontend: Thin stdio process per Claude session. Connects to daemon, proxies MCP tool calls. Returns structured data (dataclasses) for fast LLM processing.
• LSP proxy frontend: Standard LSP server over stdio. Auto-detects languages on initialize, registers projects, routes LSP requests to the correct backend. Reuses the same adapters, normalizers, and readiness tracking as MCP.

Supported Languages

Language	Default LSP Server	Autodetection	Details
C / C++	clangd	CMake, Meson, autotools, Make, Bazel	docs/c-cpp.md
Java / Kotlin	jdtls	Gradle, Maven, Ant	docs/java-kotlin.md
Python	pyright	PyBuilder, pyproject.toml, setup.py, Pipfile, requirements.txt	docs/python.md
Rust	rust-analyzer	Cargo.toml, workspace detection	docs/rust.md
Any	Custom via lsp_command parameter	—	Provide the command in lsp_register_project

Projects are autodetected when language is omitted from lsp_register_project, or inspected explicitly via lsp_detect_project. Detection scans build system markers, IDE metadata (JetBrains .idea/, Eclipse, VS Code), and source file conventions.

Requirements