github-code-search

GitHub Code Search (grep.app)

Literal code search across roughly a million public GitHub repositories. This is the fastest way to answer "has someone already done this?" — which is the question that has to be answered before any custom code gets written.

When to reach for it

• Before writing anything custom. native-first says find the existing solution first; this is how you look. A pattern with thousands of hits is idiomatic; a pattern with three is probably a mistake.
• Real usage of an API, flag, or config key the docs mention but do not show.
• Prior art for a design decision — how five projects structured the same thing.
• Error strings and stack frames — searching the literal message often lands on the upstream source that emits it.

Not for: searching this repo (use Grep), private code, or anything where the query itself is sensitive. The query string leaves the machine. Never put a hostname, credential, internal path, or customer name in a search.

How it searches

grep.app matches literal code, not keywords. It is grep over a corpus, not a search engine — there is no stemming, no synonyms, no ranking by intent. Search the exact characters you expect to be in the file.

good:  useOptimistic(          bad:  react optimistic update hook
good:  ANSIBLE_HOST_KEY_CHECKING       bad:  how to disable ansible host key checking

Primary path — the grep MCP server

One tool: mcp__grep__searchGitHub.

Param	Type	Notes
query	string	required — the literal code to find
language	string[]	e.g. ["TypeScript","TSX"], ["Nix"], ["YAML"]
repo	string	partial match — vercel/ matches the whole org
path	string	partial match — /flake.nix, /.github/workflows/
useRegexp	bool	default false; prefix (?s) for multi-line patterns
matchCase	bool	default false
matchWholeWords	bool	default false — set it when a short identifier is a substring of everything