ast-grep Structural Code Search & Rewrite

What it does

Drives ast-grep (sg) to match and rewrite code structurally: $VAR matches one AST node, $$$ matches zero or more. Ideal when the question depends on code shape rather than bytes.

• Ships a stdlib-only Python wrapper (scripts/ast_grep_helper.py) with search, replace, scan, validate, langs, doctor, and install subcommands.
• Validates patterns offline first, catching the regex-misuse mistakes (\w, .*, |) that cause most "0 matches" sessions.
• Handles ast-grep's biggest scripting gotcha automatically: --json and --update-all are mutually exclusive, so it runs a preview pass then an apply pass.
• replace is dry-run by default and always reports match count and number of files touched.
• Supports YAML rules via sg scan for reusable lint rules, auto-fixes, and CI annotations.
• Includes a decision tree for when to use ast-grep vs rg/grep vs LSP-based tooling.

Who it's for

• Engineers running large migrations (require → import, Optional[X] → X | None, API renames).
• Anyone burned by grep false positives during refactors.
• Team leads adding custom structural lint rules to CI.
• Users who want Claude Code to "change them all" without silent damage.

Examples

1. Logger migration: "Rewrite every console.log(x) to logger.info(x)" → dry-run preview with blast radius, then --apply.
2. Type cleanup: "Strip all as any casts in TypeScript and list what's left" → structural matching skips strings and comments.
3. Codebase audit: "Find empty catch blocks and turn it into a YAML rule for CI" → author a rule in rules/, run sg scan --report-style short.

Install the skill I found on Claude Skill Mart.
Copy the packages/shared-skills/skills/ast-grep folder from the GitHub repo code-yeongyu/oh-my-openagent into my ~/.claude/skills/ast-grep/.
When it's done, tell me in one line what this skill can do.