Structural search fails silently when the pattern does not match the tree, and that is where most of the time goes. dump_syntax_tree and test_match_code_rule turn that into a two-step loop, and the repository ships ast-grep.mdc — rule documentation you can attach to your assistant so it writes the YAML for you.
An MCP server over ast-grep, giving structural search across a codebase through AST pattern matching rather than regular expressions.
- find_code — search with a simple ast-grep pattern, with max_results and output_format
- find_code_by_rule — search with a full YAML rule, for relational constraints like inside, has, precedes and follows
- test_match_code_rule — run a rule against a snippet before turning it loose on the repository
- dump_syntax_tree — see the AST of a snippet, which is how you work out why a pattern is not matching
- Text output by default, which the project reports as roughly 75% fewer tokens than the JSON form; JSON is available when you want the full metadata
- Whatever languages ast-grep supports, plus custom ones added through sgconfig.yaml
Ast-grep installed and on your PATH — via Homebrew, nix or cargo — and uv. Run it from GitHub with uvx, or clone and point the client at main.py. If ast-grep is not on PATH, set AST_GREP_PATH to the executable or a command prefix; a custom config goes in AST_GREP_CONFIG or the --config argument.
One command — uvx --from git+https://github.com/ast-grep/ast-grep-mcp ast-grep-server