Skill v1.0.1

version: "1.0.1" name: refactor description: Safely refactor code with test coverage as a safety net. Use --diff to simplify just the current working diff before committing. argument-hint: "[file, function, or pattern | --diff]" disable-model-invocation: true

Refactor $ARGUMENTS safely. If $ARGUMENTS contains --diff, use Diff mode below instead.

Process

1. Understand the current state

• Read the code and its tests
• Identify what the code does, its callers, and its dependencies
• If there are no tests, WRITE TESTS FIRST. You need a safety net before changing anything

2. Plan the refactoring

• State what you're changing and why (clearer naming, reduced duplication, better structure)
• List the specific transformations (extract function, inline variable, move module, etc.)
• Check: does this change any external behavior? If yes, this isn't a refactor. Reconsider.

3. Make changes in small, testable steps

• One transformation at a time
• Run tests after EACH step. Not at the end
• If a test breaks, undo the last step and make a smaller change

4. Verify

• All existing tests pass
• Lint and typecheck pass
• The public API hasn't changed (unless that was the explicit goal)
• The code is objectively simpler. Fewer lines, fewer branches, clearer names

Diff mode (--diff): simplify what you just wrote

The pre-commit polish pass. Target = the current working diff (git diff + git diff --cached; if clean, the last commit). Goal: make the diff smaller and clearer with identical behavior.

1. Read the diff. For each hunk ask: would a reviewer write this more simply?

• Inline abstractions used once that the diff itself introduced
• Remove dead parameters, unused returns, speculative generality ("might need it later")
• Delete comments that restate the code, and defensive checks duplicating guarantees the codebase already makes
• Align naming with the surrounding file's conventions

1. Touch ONLY lines in the diff (plus mechanical consequences like an import). Never expand into surrounding code — that's regular refactor mode.
2. Show the proposed simplifications, confirm, apply in small steps, run the tests for the touched files after each.
3. Report: lines before → after. If nothing to simplify, say "diff is already minimal" and stop — don't invent work.

Rules

• If you can't run the tests, don't refactor
• Never mix refactoring with behavior changes in the same commit
• If the refactoring is large (10+ files), break it into multiple commits