ast-grep

ast-grep (sg) is a CLI tool that searches, lints, and rewrites code using Abstract Syntax Trees instead of text patterns. It uses tree-sitter parsers, supports 20+ languages (including Markdown), and runs in seconds across large codebases.

Write a code snippet as a pattern, and ast-grep matches it structurally against the AST -- ignoring whitespace, comments, and formatting differences.

Patterns are one atomic building block. When a pattern alone can't express what you need (disambiguation, naming constraints, relational checks, transforms), graduate to a full YAML rule. Patterns handle ~60% of searches; YAML rules handle the rest.