ast-grep

ast-grep (sg) is an open-source, MIT-licensed command-line tool written in Rust for searching, linting, and rewriting code by syntax structure rather than text. Patterns are written like ordinary code and matched against tree-sitter-produced syntax trees across many files. It also offers a Node.js binding for programmatic use.

What It Is

ast-grep works like a syntax-aware grep/sed. You write a code pattern, using wildcards such as $MATCH to stand for any single AST node, and the tool finds all code with the same syntactical structure. It can then rewrite the matches with a replacement pattern, either from the command line or interactively.

Search, Lint, and Rewrite Workflow

A one-line command can locate and modify code, for example rewriting $A && $A() to $A?.() in TypeScript. For linting, rules are defined in YAML configuration and run with ast-grep scan, producing formatted error reports. The project also documents an interactive codemod mode, a language server, and a testing tool for rules.

Programmatic Usage and Languages

The @ast-grep/napi package exposes syntax trees through jQuery-like traversal methods, with opt-in type safety. The site lists 20+ supported languages, and custom tree-sitter parsers can be loaded dynamically. A web playground lets users try patterns in the browser.

Installation and Intended Users

It can be installed through npm, pip, cargo, cargo-binstall, Homebrew, Scoop, MacPorts, mise, or built from source. The README says it can help library authors ship breaking-change migrations, tech leads enforce coding practices, and security researchers write rules faster.