---
name: wheel-reinvention-detector
description: "Wheel reinvention detector: harvests exported short utility functions (≤40 lines, no class state) and pairs each with the project's installed libraries (package.json, requirements.txt) plus language stdlib hints. LLM judges whether each candidate semantically duplicates an existing stdlib or library API, names the replacement, and notes behavioral differences. Read-only. Audience: Both. Trigger: /reinvented-wheels"
trigger: /reinvented-wheels
---

## What this is for

Every codebase hides hand-rolled versions of `Array.prototype.flat`,
`lodash.groupBy`, `path.Combine`, or `retry-with-backoff`. Each one is
untested surface area a maintained library already solved. The collector
extracts short exported utility functions and pairs them with the project's
installed dependencies; the LLM recognizes semantic equivalence and names
the replacement.

Single lint rules exist for narrow cases (`unicorn/prefer-native`). No general
"did you mean to use the library you installed" detector exists before this.


## PROTECTION RULE - never ~/.claude/

Read-only skill. Guard required if write mode added later.

## ## What You Must Do When Invoked
During analysis, assign a confidence level to each finding: proven (confirmed by evidence), likely (strong signal, needs review), or suspected (weak signal).

### Step 1

1. If `-help` is passed, print the `## Usage` block below and stop.

### Step 2

2. Confirm `-ProjectDir` is provided and the path exists.

### Step 3

3. Run: `scripts/util-harvest.ps1 -ProjectDir "<path>"`

### Step 4

4. LLM reads the JSON output. For each candidate short utility:

### Step 5

- Read the function body.

### Step 6

- Is this semantically equivalent to a stdlib feature of the language

### Step 7

version, or to an API of an installed library?

### Step 8

- Name the exact replacement (function or method).

### Step 9

- Note behavioral differences: edge cases the custom version catches or

### Step 10

misses compared to the library equivalent.

### Step 11

5. Classify: `reinvented-stdlib` / `reinvented-library` / `custom-domain`

### Step 12

(legitimate, do not replace).

### Step 13

6. Write `reinvented-wheels-report.md` to the working directory.

## Usage

```
/reinvented-wheels                             # interactive
/reinvented-wheels <dir>                       # scan project directory
/reinvented-wheels -help                       # show usage
```

Returns JSON with `candidates[]` (short util functions), `installedLibs[]`,
`semanticHints{}`, plus summary counts.