| name | codebase-hygiene |
| description | Find semantic duplicates (same intent, different implementation) and shallow modules (thin wrappers spreading complexity). Read-only advisory — changes route through BUILD with full gates. Use when auditing code quality, before refactoring, or when a codebase feels bloated. |
Codebase Hygiene
Advisory and read-only. Diagnoses and proposes; does not refactor. Any actual change: tell the user to run /build.
Mode 1: Semantic duplicate detection
Copy-paste detectors catch syntactic duplicates. This finds semantic duplicates — functions serving the same purpose but implemented independently under different names.
Method
- Extract catalog — grep/glob for exported functions. Record
name | file:line | signature.
- Categorize by domain (cheap tier) — validation, formatting, path manipulation, HTTP shaping, date handling. Mechanical bucketing to shrink the comparison space.
- Drop categories with <3 functions — can't hide a meaningful duplication pattern.
- Detect duplicates per category (capable tier) — READ the implementations, decide which share intent. Never use cheap name-based detection — it anchors on names and rubber-stamps "these look different."
- Emit findings — group by confidence, highest first. Each finding: what is duplicated, why it matters, the fix,
file:line evidence. Route through the review finding contract.
High-risk zones
| Zone | Why it duplicates |
|---|
utils/, helpers/, lib/ | Catch-all dumping grounds |
| Validation code | "Is this a valid email/id/url" rewritten per feature |
| Error formatting | Every module invents its own Error → string |
| Path manipulation | Join/normalize/relativize reimplemented |
| String formatting | Truncate, slugify, titlecase, pad re-rolled |
| Date formatting | Parse/format/diff scattered |
| API response shaping | Envelope/pagination/error-body copied per endpoint |
Consolidation discipline
Never delete a duplicate until ALL THREE hold:
- Survivor has tests — pick the implementation with real coverage. If neither has tests, write the test against the chosen survivor first.
- All callers updated — grep to enumerate callers. Missing one is a silent break.
- Re-run after consolidation — test suite + build/typecheck pass. Green tests on the survivor license the deletion.
Mode 2: Module deepening
Thin wrappers and pass-through layers spread complexity without adding capability. A module that only forwards calls to another module is a shallow module — it adds a layer to navigate without earning it.
Signals
- A module whose entire body is forwarding calls to one other module.
- "Manager" / "Service" / "Helper" classes that wrap a single dependency and add no logic.
- Functions that take args, immediately pass them unchanged to another function, and return its result.
Fix direction
Deepen: collapse the wrapper into its caller, OR add real responsibility (validation, transformation, policy) that justifies the layer. A module should either hide complexity (deep module) or not exist.
Don't
- Don't refactor from this skill — it's advisory. Propose, then tell the user to run
/build.
- Don't delete a duplicate without the 3 consolidation gates (tests + callers + re-run).
- Don't trust name-based duplicate detection — read the implementations.
