Code Review Mastery

Code Review Mastery

Complete code review lifecycle: WHAT to check, HOW to interact, and WHEN to verify.

Overview

Code review is a three-part discipline:

1. WHAT to Review - Security, logic, clean code, metrics
2. HOW to Interact - Receiving feedback, requesting reviews, giving feedback
3. VERIFICATION - Evidence before any completion claims

Quick Start

Giving a Review

Priority order: Security > Correctness > Maintainability > Performance

1. SECURITY: Input validation, auth checks, secrets exposure
2. LOGIC: Edge cases, error handling, null checks
3. ARCHITECTURE: Single responsibility, proper abstractions
4. TESTS: Coverage for new functionality

Skip (automate instead): Formatting, naming conventions, linting violations

Receiving Feedback

READ → UNDERSTAND → VERIFY → EVALUATE → RESPOND → IMPLEMENT

• No performative agreement ("You're absolutely right!")
• Verify against codebase before implementing
• Push back if technically wrong

Before Claiming Done

NO COMPLETION CLAIMS WITHOUT FRESH VERIFICATION EVIDENCE

Run the command. Read the output. THEN claim the result.

Part 1: What to Review

Security (Critical)

Must check in every review:

• No hardcoded credentials (search: password.*=.*['"], api[_-]?key.*=)
• Input validation on all user data
• Parameterized queries (no string concatenation for SQL)
• Authorization checks on every endpoint
• No eval(), exec(), dangerous functions

Reference: references/security-checklist.md

Logic (Critical)

Verify correctness:

• Business logic matches requirements
• Edge cases handled (null, empty, boundary values)
• Error handling present and appropriate
• Race conditions in async code
• Resource cleanup (connections, file handles)

Clean Code (High)

Check for code smells:

• Large functions (>50 lines) - violate Single Responsibility
• Deep nesting (>3 levels) - extract to functions
• Long parameter lists (>3 params) - use objects
• Duplicated code - extract to shared functions
• Magic numbers/strings - use named constants

Reference: references/clean-code-principles.md

Metrics (Medium)

Targets:

Reference: references/code-quality-metrics.md

Part 2: How to Interact

Giving Feedback

Structure: What + Why + How

✓ "[BLOCKING] SQL injection at line 34. Query uses string concatenation
   with user input. Fix: Use parameterized query:
   db.query('SELECT * FROM users WHERE id = ?', [userId])"

✗ "This query looks unsafe."

Priority Labels:

Reference: references/feedback-patterns.md

Receiving Feedback

The Response Pattern:

1. READ: Complete feedback without reacting
2. UNDERSTAND: Restate requirement in own words
3. VERIFY: Check against codebase reality
4. EVALUATE: Technically sound for THIS codebase?
5. RESPOND: Technical acknowledgment or reasoned pushback
6. IMPLEMENT: One item at a time, test each

Forbidden responses:

• "You're absolutely right!" (performative)
• "Great point!" (performative)
• "Let me implement that now" (before verification)

When feedback is unclear:

STOP - do not implement anything yet
ASK for clarification on ALL unclear items

When feedback is wrong: Push back with technical reasoning, not defensiveness.

Reference: references/code-review-reception.md

Requesting Review

When to request:

• After each task in subagent-driven development
• After completing major features
• Before merge to main

How:

BASE_SHA=$(git rev-parse HEAD~1)
HEAD_SHA=$(git rev-parse HEAD)

Then dispatch code-reviewer subagent via Task tool.

Reference: references/requesting-code-review.md

Part 3: Verification Gates

The Iron Law

NO COMPLETION CLAIMS WITHOUT FRESH VERIFICATION EVIDENCE

The Gate Function

1. IDENTIFY: What command proves this claim?
2. RUN: Execute the FULL command (fresh, complete)
3. READ: Full output, check exit code, count failures
4. VERIFY: Does output confirm the claim?
5. ONLY THEN: Make the claim

Common Failures

Red Flags - STOP

• Using "should", "probably", "seems to"
• Expressing satisfaction before verification
• About to commit without running tests
• ANY wording implying success without evidence

Reference: references/verification-before-completion.md

Anti-Patterns

Nitpicking

Problem: Excessive minor comments bury critical issues Solution: Automate style with linters; focus humans on logic/security

Vague Criticism

Problem: "This is wrong" without explanation Solution: Always include What + Why + How

Blocking on Preferences

Problem: Blocking merge for subjective style Solution: Reserve blocking for security/correctness only

Performative Agreement

Problem: "You're absolutely right!" without verification Solution: Verify first, then implement

Decision Tree

SITUATION?
│
├─ Reviewing someone's code
│  ├─ Security issue? → [BLOCKING] with fix
│  ├─ Logic bug? → [BLOCKING] with test case
│  ├─ Code smell? → [SUGGESTION] with explanation
│  └─ Style preference? → Skip or automate
│
├─ Received feedback
│  ├─ Unclear items? → STOP, ask for clarification first
│  ├─ From trusted source? → Understand, then implement
│  └─ From external reviewer? → Verify technically before implementing
│
├─ Completed work
│  └─ Major feature/task? → Request code-reviewer subagent review
│
└─ About to claim status
   ├─ Have fresh verification? → State claim WITH evidence
   └─ No fresh verification? → RUN command first

Reference Guides

• Security: references/security-checklist.md - OWASP Top 10, auth, input validation
• Clean Code: references/clean-code-principles.md - SOLID, naming, functions, smells
• Feedback: references/feedback-patterns.md - Valuable vs wasteful patterns
• Metrics: references/code-quality-metrics.md - Complexity, maintainability
• Reception: references/code-review-reception.md - How to receive feedback
• Requesting: references/requesting-code-review.md - How to request reviews
• Verification: references/verification-before-completion.md - Evidence gates

Success Criteria

A good code review:

• Identifies security vulnerabilities (if any)
• Catches logic errors and edge cases
• Flags maintainability issues with specific fixes
• Uses priority labels ([BLOCKING] vs [SUGGESTION])
• Provides actionable feedback (What + Why + How)
• Avoids nitpicks on style/formatting
• Verifies claims with evidence before completion