Investigate code with the lsp tool, which uses a language server to understand names, imports, and types. Find definitions and usages, inspect signatures and file outlines, and check compiler or type errors after edits.
Recipes for the lsp tool — resolving where a symbol is defined, every place it is used, type signatures and docs, file outlines, and compiler/type errors through a real language server (Go, TypeScript/JavaScript, Python, Rust). Use when navigating or explaining code by symbol, finding callers or usages, checking what broke after an edit, or deciding between lsp and text search.
Review the instructions the agent will receive before you install.
The lsp tool answers semantic questions through the language's own server:
it resolves through imports, types, and aliases, where grep only matches text.
Reach for it whenever the question is about a symbol; keep grep for plain
strings, comments, and file types no server supports.
| Operation | Answers | Needs |
|---|---|---|
definition | where the symbol at a position is defined | path, line, column |
references | every place the symbol at a position is used | path, line, column |
hover | type signature + docs for the symbol at a position | path, line, column |
documentSymbol | the outline (types, functions, methods) of one file | path |
diagnostics | compiler/type errors and warnings for one file | path |
Positions are 1-based, and column must point at the identifier (its first
character works). All paths resolve against the working directory.
"Where is X defined?" — from any usage site of X:
{"operation": "definition", "path": "<file>", "line": <L>, "column": <C>}.
Don't know a usage site? Find one first (see next recipe's step 1).
"Everywhere X is used" — two steps, always:
rg -n --column '\bX\b' (the --column output is
exactly the coordinate the next call needs), or documentSymbol when you
already know the file.{"operation": "references", "path": "<decl file>", "line": <L>, "column": <C>}.A grep hit list is not a references answer: it includes comments and strings, misses aliased imports, and can't distinguish same-named symbols. Step 2 is what makes the answer authoritative.
"What is this / what's its signature?" — hover at the symbol. Prefer it
over reading the definition file when you only need the type or doc comment.
"What's in this file?" — documentSymbol before reading a large file; jump
straight to the line the outline gives you.
"Did my edit break anything here?" — diagnostics on the file after
editing. It reports the server's current analysis of the saved file.
lsp_enable (see the install-lsps skill for
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Set up language servers, programs that help tools understand source code, for Go, TypeScript, Python, and Rust. Check missing prerequisites, install them with approval, and verify the lsp tool against a real source file.