Introduction
mcpls gives an AI coding assistant the same understanding of your code that your editor has. Instead of reading source files as plain text, the assistant can ask a compiler-grade question and get a precise answer: what is the type of this variable, where is this function defined, who calls it, and what errors does the compiler report right now.
The problem
An AI assistant without code intelligence works with text. To answer “where is ApiError::Timeout handled?” it searches for strings, guesses which matches are real, and misses the ones that go through aliases or re-exports.
Your editor does not guess. It talks to a language server (rust-analyzer, pyright, gopls, and others) over the Language Server Protocol (LSP), which knows the real structure of the project.
What mcpls does
mcpls is a bridge. It speaks the Model Context Protocol (MCP) to your AI client and the Language Server Protocol (LSP) to the language servers:
flowchart LR
C["AI client"] <-->|MCP| M["mcpls"] <-->|LSP| S["rust-analyzer / pyright / gopls / ..."]
It starts the language servers it needs for your project, translates every question into LSP, and returns the answer in a form the assistant can use. It exposes 31 tools, from get_hover and get_references to rename_symbol and get_diagnostics.
What you get
- Type information. Ask what a variable or expression is, with documentation.
- Cross-references. Find every real usage of a symbol across the workspace.
- Semantic navigation. Jump to definitions, implementations, type definitions and declarations.
- Real diagnostics. Read the errors and warnings the compiler or linter reports, not guesses.
- Safe refactoring. Get a workspace-wide rename plan as a set of edits.
mcpls does not change your files. Tools such as rename_symbol and format_document return edits for the assistant to apply; every other tool is read-only.
How this book is organized
The book follows a path from first use to deep detail. Read as far as you need.
| Part | Read it when you want to | Outcome |
|---|---|---|
| Part 1: Quick Start | Try mcpls | A working setup and your first answer in minutes |
| Part 2: Everyday Use | Use it on real projects | Configured servers, a tour of every tool, and fixes for common problems |
| Part 3: Under the Hood | Understand or harden a deployment | Architecture, positions, lifecycle, HTTP transport, security model |
| Reference | Look something up | Every flag, environment variable and configuration key |
What’s Next
Start with Installation to get the mcpls binary onto your machine.