Codemods & AST Tools

When you need to upgrade 200 files, swap an API across a monorepo, or migrate to a new framework version, AST tools beat regex.

TypeScript / JavaScript AST

• ★ ts-morph — high-level TypeScript Compiler API wrapper. The default when you need full type info during transformation.
• ★ jscodeshift (Meta) — the codemod runner; ships with React's official codemods. Lower-level than ts-morph.
• @babel/core + @babel/parser — when you need full Babel ecosystem.
• swc + @swc/wasm-web — Rust-based parser; very fast.
• OXC — fastest JS toolchain (parser, transformer, linter). Used inside oxlint.
• Recast — preserves formatting in AST output.
• Prettier as a step at the end — re-format whatever you generated.

High-level codemod orchestration

• ★ codemod.com / Intuita — registry of codemods + a runner; codemod CLI applies framework / library upgrades. The default in 2026.
• @codemod/cli — runs jscodeshift, ts-morph, ast-grep recipes uniformly.
• grit — pattern-based transforms; SQL-like for code.
• semgrep — pattern-based code search + autofix; great for security and style rules.

Tree-sitter / multi-language

• ★ tree-sitter — incremental parser for many languages; bindings for everything.
• ★ ast-grep (sg) — Rust CLI for tree-sitter pattern matching; "grep with structure." Excellent for cross-language refactors.
• comby — alternative pattern-based rewrite tool.
• GritQL — Grit's query language.

CSS / config / docs AST

• PostCSS — CSS AST.
• stylelint — CSS lint rules / autofix.
• YAML AST: yaml (eemeli/yaml package) preserves comments.
• TOML AST: @iarna/toml etc.
• JSON5 for JSON-with-comments parsing.
• mdast / hast / xast — markdown / HTML / XML ASTs (used by remark / rehype).

Auto-fix in editors

• ESLint --fix — your existing rules already do half this work.
• Biome — formatter + linter with autofix.
• dprint — formatter with plugin system.

When to reach for codemods

• Migrating Next.js 15 → 16 or Astro 5 → 6 — official codemods exist.
• Renaming a hook / API across hundreds of files.
• Converting import patterns (default → named).
• Removing dead feature-flag branches after a flag is fully rolled out.
• Adopting a new validation library (Zod → Valibot, etc.).

When not to

• "Find a string and replace it" — use sed / rg --replace.
• One-off renames in 5 files — let your editor do it.
• Truly novel transformations specific to your domain — sometimes a quick script is faster than learning ts-morph.

Pick this if…

• Default upgrade-from-X-to-Y: check codemod.com first; the codemod likely exists.
• Type-aware transformation: ts-morph.
• Cross-language pattern rewrite: ast-grep.
• Security / style rules with autofix: semgrep.
• Formatting after transform: Prettier or Biome.