ast-grep - SKILL.md Agent Skill

name: ast-grep description: AST-based code search and transformation tool using tree-sitter. Use for structural pattern matching, refactoring deprecated APIs, detecting anti-patterns, migrating code between library versions, and enforcing coding standards.

ast-grep - AST-based Code Search and Transformation

ast-grep is an AST-based tool for searching, linting, and refactoring code across multiple languages. It uses tree-sitter to parse code into Abstract Syntax Trees, enabling precise structural pattern matching.

Key Pattern Syntax

$META - Matches a single AST node (e.g., $VAR, $FUNC, $ARG)
$$$ - Matches zero or more AST nodes (useful for function arguments, statements)
$_ - Non-capturing metavariable (matches but doesn't capture)
Patterns must be syntactically valid code in the target language

Triggers

AST pattern, structural search, code refactoring, find anti-patterns, migrate code, console.log, deprecated API, function definition, class search, method signature, unused variables, security vulnerabilities, code transformation, pattern matching

When to Use

Finding specific code patterns across large codebases
Refactoring code (replacing deprecated APIs, updating syntax)
Detecting anti-patterns or potential bugs
Migrating between library versions
Enforcing coding standards
Interactive code rewriting

Examples

I need to find all React components using useState I'll find useState usage in React components: `ast-grep --pattern 'const [$STATE, $SETTER] = useState($$$)'` Replace && chains with optional chaining for null checks I'll modernize null checks to optional chaining: `ast-grep --pattern '$OBJ && $OBJ.$PROP' --rewrite '$OBJ?.$PROP' --interactive` Find async functions that don't have error handling I'll search for async functions without try-catch: `ast-grep --pattern 'async function $NAME($$$PARAMS) { $$$BODY }' | grep -v try` Find all TypeScript interfaces I'll search for TypeScript interfaces: `ast-grep --pattern 'interface $NAME { $$$BODY }' --lang ts` I want to find potential null pointer exceptions I'll search for property access without null checks: `ast-grep --pattern '$VAR.$PROP' --filter 'not match { $VAR?.$PROP }'`