ast-grep Structural Code Search and Rewrite
Use ast-grep (sg) to search, lint, and rewrite code across large codebases using AST pattern matching. A blazing-fast alternative to regex-based code transformations that understands syntax structure.
npx skills add agentskillexchange/skills --skill ast-grep-structural-code-search-rewrite
ast-grep is a CLI tool for code structural search, linting, and rewriting built on top of tree-sitter. Unlike traditional text-based grep or regex tools, ast-grep operates on abstract syntax trees (ASTs), meaning it understands the syntactic structure of your code rather than just matching character patterns.
What this skill actually does
Overview
With ast-grep, you write search patterns as ordinary code using dollar-sign meta-variables (e.g., $MATCH) as wildcards that match any single AST node. This makes complex code transformations intuitive — you describe the pattern you want to find and what you want to replace it with, and ast-grep handles the rest across entire codebases.
How It Works
The skill wraps the @ast-grep/cli package (also available via pip, cargo, homebrew, and other package managers). Agents can use ast-grep to perform large-scale code migrations, enforce custom lint rules via YAML configuration, and execute interactive search-and-replace sessions across multiple files and languages including TypeScript, JavaScript, Python, Rust, Go, Java, and more.
A typical workflow involves running ast-grep -p '$A && $A()' -r '$A?.()' -l ts to find and rewrite patterns like optional chaining conversions. For linting, teams define rules in YAML that describe forbidden patterns and their suggested fixes, getting pretty error reporting out of the box.
Key Capabilities
ast-grep produces structured output (JSON, SARIF) suitable for CI/CD integration and automated code review pipelines. It supports jQuery-like API traversal for programmatic AST manipulation via its Node.js bindings. The tool is written in Rust and compiles to native code, delivering performance orders of magnitude faster than JavaScript-based AST tools. With over 13,000 GitHub stars and active development, ast-grep is used by teams for codemod operations, enforcing coding conventions, and building custom static analysis rules.