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helderbertohelderberto/agent-skills/skills/refactor/SKILL.md

refactor

Skill19 starsChanged 32 days agoMITView on GitHub

Improve existing code without changing behavior — split large functions, backfill tests, simplify. Use when asked to "refactor", "add missing tests", "split functions", "simplify", "clean up code", or "reduce complexity". Don't use for new features (/tdd), security hardening (/harden), or PR review (/code-review).

196 other projects use a version of this.

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The file

We split this skill into the rules it gives an agent

2 rules. 0 are common, 2 are distinctive, and 0 are very specific to this project.

  • 0

    Common

    Most of the 169 edited versions we read keep these.

  • 2

    Distinctive

    This author's own choices. Worth a look.

  • 0

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Distinctive:

    Run the suite. If red, stop — don't refactor broken code

    line 19
  2. Distinctive:

    Chesterton's Fence: before removing anything, explain why it's there.

    line 32

“Common” is measured: kept by at least 6 in 10 of the 169 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Refactor

Target: $ARGUMENTS (file, directory, or module — if blank, use unstaged changes)

Behavior is frozen — the test suite is the contract. Green before and after; if a test's meaning has to change, you've gone too far.

Workflow

1. Scope

  • Identify target files (blank → unstaged changes)
  • Locate each file's tests using the project's convention (co-located, __tests__/, tests/, spec/). A file with no tests gets Test gaps items first — Split/Simplify on untested code is unverifiable, so backfill or skip. No test runner at all → ask which to use. UI flows → backfill end-to-end tests: call the Skill tool with tdd, which holds the UI-tests reference. Entrypoint scripts without exports → audit only.
  • Run the suite. If red, stop — don't refactor broken code

2. Audit

List findings, most-impactful first:

BucketWhat to look forFix
SplitFunctions > 20 lines, multiple responsibilities, I/O mixed with logicExtract pure logic into named helpers; keep I/O at the edges; preserve the original signature
Edge casesMissing null/empty/boundary checks at system boundaries, unhandled error pathsTest first, then guard
Test gapsUntested public functions, uncovered branches, missing sad-path testsBackfill through the public interface
SimplifyNesting > 2 levels, dead code / unused params, duplicated logic, dense one-liners, shallow pass-through wrappers, speculative config never used, unclear names / primitive obsessionGuard clauses, delete, extract one helper, expand, inline (call the Skill tool with codebase-design for the deletion test), remove, rename to intent / small type

Chesterton's Fence: before removing anything, explain why it's there. If you can't, leave it and flag it.

Present the audit as a checklist and ask which items to address — "All items" first, marked (Recommended).

3. Apply — one item at a time

Per approved item: RED (failing test exposing the gap, when the item adds behavior coverage) → GREEN (minimal change) → run tests. Real values over mocks; mock only external I/O (call the Skill tool with tdd for its mocking guide). If red after the change, revert it and flag as blocked. Never batch.

4. Report

Items addressed, tests added, functions extracted, items skipped with reason (Chesterton), suite result before/after.

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