Code Reviewer Skill

Before Reviewing

1. Gather context – Read related files to understand existing patterns, naming conventions, and architectural decisions in the codebase.
2. Run automated checks – If available, run linters, type-checkers, and tests to catch mechanical issues first.
3. Understand the change – Identify the purpose of the change (bug fix, feature, refactor) to calibrate the review appropriately.
4. Check git history – For non-trivial changes, review git blame on modified sections to understand why code exists, past bug fixes that might be undone, and related commits that provide context.

Evaluation Criteria

Review the code against these categories:

1. Correctness – Logic bugs, incorrect assumptions, unhandled edge cases, race conditions, error handling gaps.

2. Security – Injection risks, authentication/authorization flaws, sensitive data exposure, unsafe dependencies.

3. Performance – Algorithmic complexity, N+1 queries, memory leaks, unnecessary computation, missing caching opportunities.

4. Maintainability – Code clarity, naming, complexity, duplication, testability, documentation.

5. Architecture – Modularity, separation of concerns, appropriate abstractions, dependency direction.

6. Testing – Test coverage for new code, test quality, edge case coverage.

7. Local Standards – Adherence to project conventions, patterns, and style guides found in the codebase.

8. Breaking Changes – API compatibility, migration requirements, backwards compatibility (when applicable).

9. CLAUDE.md Compliance – Check changes against CLAUDE.md files in:

   • Repository root
   • Directories containing modified files
   • Parent directories of modified files

   Only flag violations explicitly stated in CLAUDE.md. Quote the guideline when flagging.

Output Format

Summary

Brief overview of the change quality and key concerns.

What's Done Well

Highlight 1–3 positive aspects worth preserving or replicating.

Findings

Organize findings by severity (only report issues with confidence ≥50):

• 🔴 Critical (confidence%) – Must fix before merge (security, data loss, crashes)
• 🟠 Major (confidence%) – Should fix, significant quality/maintainability impact
• 🟡 Minor (confidence%) – Suggested improvements, lower priority
• ⚪ Nit (confidence%) – Style preferences, optional polish

For each finding include:

• File and line reference (e.g., src/auth.ts:42)
• Confidence score (0-100) with brief rationale
• Clear description of the issue
• Concrete suggestion for fixing it
• CLAUDE.md reference if applicable (quote the specific guideline)

Confidence scale:

• 90-100: Verified real issue, will cause problems in practice
• 70-89: Likely real issue, worth fixing
• 50-69: Possibly real, author should evaluate
• Below 50: Do not report – too uncertain

Pre-existing Issues Worth Noting

(Optional) Issues spotted that predate this change – for awareness only.

Recommended Next Steps

Prioritized action items for the author.

What NOT to Flag

Avoid false positives by NOT flagging:

• Pre-existing issues not introduced by this change
• Issues that linters, type-checkers, or tests will catch
• Pedantic nitpicks a senior engineer wouldn't mention
• General code quality concerns (unless explicitly required in CLAUDE.md)
• Issues with lint ignore comments or explicit suppressions
• Changes in functionality that are clearly intentional
• Issues on lines the author didn't modify in this change

Scope of Review

• Focus ONLY on code that was added or modified in this change
• If you spot a pre-existing issue, note it separately under "Pre-existing Issues Worth Noting" but do NOT include in the main findings
• When in doubt whether an issue is new or pre-existing, check the diff carefully – if the line wasn't touched, don't flag it

Guidelines

• Focus primarily on the changed code, but flag systemic issues if they impact the change.
• Be specific and actionable — avoid vague feedback like "make this cleaner".
• If context is ambiguous or the change purpose is unclear, ask clarifying questions before finalizing.
• Calibrate depth to change size: see "Review Depth Calibration" below.

Review Depth Calibration

Adjust review intensity based on change scope:

• Light review (1-3 files, simple change): Summary + key findings only. Skip "What's Done Well" if nothing notable.
• Standard review (4-10 files, feature or refactor): Full template with all sections.
• Deep review (security-adjacent changes — auth, payments, data access, crypto): Full template + explicit security section. Always use full depth regardless of file count.

Examples

WRONG vs. CORRECT: Writing Findings

WRONG — vague finding:

🟠 Major — This function could have issues with error handling.

CORRECT — actionable finding with evidence:

🟠 Major (82%) src/api/users.ts:47 — fetchUser swallows the database error and returns null, making it impossible for callers to distinguish "user not found" from "database unreachable." Return a Result<User, DbError> or rethrow with context.

WRONG vs. CORRECT: Scope Discipline

WRONG — flagging pre-existing code outside the diff:

🟡 Minor — The logger module on line 12 uses console.log instead of a structured logger. (Line 12 was not modified in this change.)

CORRECT — respecting diff boundaries:

(Line 12 was not modified — no finding reported. If important, noted under "Pre-existing Issues Worth Noting.")

Pre-Delivery Checklist

Before presenting a review, verify:

• Every finding includes a file:line reference
• Every finding includes a confidence percentage
• No findings flag lines outside the diff (scope discipline)
• CLAUDE.md guidelines are quoted verbatim when cited
• "What's Done Well" items are specific, not generic praise
• Review depth matches change scope (light/standard/deep)
• Pre-existing issues are in their own section, not main findings