Codemod

This gives Claude systematic knowledge about writing AST-based code transformations using tools like ast-grep and JSSG. The skill covers 48 rules across pattern matching, node traversal, semantic analysis, and edit operations, all prioritized by impact. You'd want this when building codemods for automated refactoring, migrating codebases between API versions, or debugging why your transformation is matching the wrong nodes. The focus on idempotency, batched edits, and test fixtures shows real production experience. One thing that stands out is the emphasis on exploring ASTs before writing patterns and using constraints to avoid overly generic matches, which are exactly the mistakes that lead to broken migrations at scale.