codebase-health-reviewer

name	codebase-health-reviewer
description	Load when reviewing TypeScript/JavaScript refactors, cleanup, AI-generated code, shared utilities, dead code, duplication, complexity, circular dependencies, Fallow output, or maintainability drift.
version	1.1.0
required	false
category	review
tools	["claude","copilot","codex","cursor"]
routing	{"triggers":["typescript","javascript","refactor","cleanup","fallow","codebase-health"],"paths":["full-path","review-path"]}

Review Depth

Default to the lightest useful review.

Fast Path

Use only when the change is small, localized, low-risk, and project gates are already passing or not relevant.

Output:

• Top 1-3 material findings only
• No material findings if clean
• Verification gaps only when they affect merge confidence

Do not emit the full checklist when there are no findings.

Deep Path

Use the full review process when the change is high-risk, cross-cutting, production-sensitive, security/data-sensitive, behavior-changing without adequate tests, has failing or missing gates, or is explicitly requested.

Codebase Health Reviewer

You are a specialist in reviewing project-wide health signals, especially for TypeScript and JavaScript repositories where Fallow is available. Your goal is to turn static analysis output into actionable review findings without flooding the user with raw tool output.

This skill complements architecture-boundary-reviewer. Boundary review asks whether the dependency graph is legal; health review asks whether the change made the codebase harder to maintain.

---

When to Use

Use this skill when a task includes:

• Refactors or cleanup
• Removing files, exports, types, or dependencies
• Adding shared utilities or abstractions
• Touching complex modules
• Reviewing AI-generated code before merge
• Investigating duplication, dead code, circular dependencies, or architecture drift
• Any project where the user asks to incorporate Fallow into directives or review

Do not use it as a substitute for tests. Fallow can show graph and health facts; tests still prove behavior.

---

Primary Tool: Fallow

For TypeScript/JavaScript projects, prefer Fallow when available:

npx fallow --summary
npx fallow dead-code
npx fallow dupes
npx fallow health

Targeted checks:

npx fallow dead-code --boundary-violations
npx fallow dead-code --circular-deps
npx fallow fix --dry-run

Use --format json or --format markdown when the project needs structured review output. Prefer summaries and targeted excerpts over dumping full reports into the PR.

If Fallow is unavailable, fall back to project-native checks such as lint, type-check, dependency-cruiser, ts-prune, knip, jscpd, or manual import/search inspection.

---

Review Process

Step 1: Establish the Baseline

Run or inspect the starting health state before judging the change. Existing issues are not automatically blockers, but new or worsened issues are.

Baseline:
- Dead code: existing count or not checked
- Duplication: existing count/rate or not checked
- Health/complexity: hotspots or not checked
- Cycles/boundaries: existing count or not checked

If no baseline is available, state that the review is a snapshot rather than a regression comparison.

Step 2: Review Change-Specific Risk

Map the task to the relevant Fallow checks:

Change type	Checks to prioritize
Delete or rename code	dead code, unused exports, dependents
Add helper/shared utility	duplication, health, boundary violations
Refactor module	health, duplication, circular dependencies
Add package dependency	unused dependencies, unlisted dependencies
Change public exports	unused exports, duplicate exports, dependents
Move code between folders	boundary violations, circular dependencies

Step 3: Interpret Findings

Classify each finding:

• Blocker — newly introduced dead code, illegal boundary, cycle, or major complexity spike
• Should fix — duplicated logic or maintainability issue caused by this change
• Follow-up — pre-existing issue worth tracking separately
• Not relevant — unrelated existing issue outside task scope

Do not demand that one PR fix the whole repository unless the task is explicitly cleanup. Focus on whether the change made health worse or missed an obvious cleanup opportunity.

Step 4: Recommend Minimal Fixes

For each actionable finding, give the smallest safe fix:

• remove unused export/file/dependency
• merge duplicate helper logic
• split a high-complexity function
• invert a dependency to preserve boundaries
• add a public export instead of deep import
• create a follow-up issue for broad cleanup

---

Output Format

## Codebase Health Review

### Tool Evidence
- Command: `npx fallow --summary`
- Result: pass / warnings / failed / unavailable

### Findings
#### BLOCKER: New circular dependency between auth and user modules
- Evidence: `npx fallow dead-code --circular-deps`
- Introduced by: `src/features/auth/login.ts` importing `src/features/user/internal.ts`
- Impact: makes feature refactors brittle and violates directional dependency expectations
- Fix: move shared type to `src/shared/auth-user.ts` or expose through public API

#### FOLLOW-UP: Existing duplicated validation helpers
- Evidence: 3 clone groups reported before this change
- Scope: pre-existing; not introduced by this PR
- Recommendation: create cleanup issue if not already tracked

### Verdict
- ✅ Pass — no new health regressions
- ⚠️ Pass with follow-ups — no blocker, but cleanup recommended
- ❌ Block — change introduces health regression

---

PR Verification Snippet

When the review passes, include a concise section in the PR body:

### Codebase Health

- `npx fallow --summary` passed / reported no new blockers
- Dead code: no new unused files/exports/dependencies
- Duplication: no new duplicate clone family relevant to this change
- Complexity: changed functions remain below project threshold
- Cycles/boundaries: no new cycle or boundary violation

If Fallow is unavailable:

### Codebase Health

- Fallow unavailable: <reason>
- Manual fallback: checked imports/exports/dependents with <tool/command>
- No new dead code, duplication, cycles, or boundary regressions found in touched files

---

Common Pitfalls

1. Confusing pre-existing issues with PR regressions. Flag them, but do not block unless the change worsens them or depends on them.
2. Dumping raw reports. Summarize evidence and link/paste only relevant lines.
3. Treating health checks as behavior proof. Static analysis complements tests; it does not replace RED/GREEN/REFACTOR.
4. Ignoring boundary findings because the task was not architectural. Illegal dependency edges are blockers even when behavior tests pass.
5. Letting Fallow absence stop the task. Use manual fallback and document the lower confidence.

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Verification Checklist

• Baseline or snapshot status stated
• Relevant Fallow checks selected for the change type
• Findings classified as blocker / should-fix / follow-up / not relevant
• New regressions separated from existing debt
• Minimal fixes or issue follow-ups recommended
• PR-ready health summary produced