The LSP tool wires Claude into the same Language Server Protocol your IDE uses. That means real "jump to definition" and "find references", not regex guesses.

What it does

Claude Code talks to your project's installed language servers to resolve symbols, find references, pull type info, and report diagnostics. When you ask "where is this function used?", the LSP returns real call sites from the compiler, not a Grep that might catch comments or strings.

When to use it

Any task involving TypeScript, Python, Rust, Go, or other LSP-supported languages.
Refactors where you need to hit every real reference.
Investigating type errors or diagnostics.
Understanding unfamiliar code with precise navigation.

Gotchas

The language server has to be installed and runnable in your environment.
First-run indexing can be slow on large monorepos. Subsequent queries are fast.
Some languages have thin LSP support - fall back to Grep if definitions come back empty.

Official docs: https://code.claude.com/docs/en/tools-reference.md#lsp-tool-behavior