Code review is one of the highest-leverage activities in software development — and one of the most inconsistent. Senior engineers do it well. Junior engineers struggle with the scope. Everyone does it differently.
Claude Code changes that. You can now run a complete code review — catching bugs, logic errors, security issues, and style violations — in under 30 seconds, before the PR even lands in a human reviewer's queue.
This guide covers how to set it up, what to ask Claude, and how to build a review workflow that actually improves your codebase over time.
AI code review is not about replacing human judgment. It's about eliminating the 80% of review work that's mechanical: does this code handle null inputs? Is this SQL query vulnerable to injection? Does this function do what its name says?
Human reviewers are good at: architecture decisions, business logic correctness, team conventions, intent vs. implementation gaps.
Claude Code is good at: everything else.
| Review Category | Claude Code | Human Reviewer |
|---|---|---|
| Null/undefined handling | ✅ Excellent | Often missed when tired |
| Security patterns (SQLi, XSS, etc.) | ✅ Excellent | Requires security expertise |
| Error handling coverage | ✅ Excellent | Easy to skip |
| Code style consistency | ✅ Excellent | Slow, subjective |
| Test coverage gaps | ✅ Good | Depends on reviewer |
| Business logic correctness | ⚠️ Limited (needs context) | ✅ Essential |
| Architectural decisions | ⚠️ Limited | ✅ Essential |
| Team convention violations | ✅ If defined in CLAUDE.md | ✅ If reviewer knows them |
The best workflow: Claude runs first, catches the mechanical issues, humans focus on logic and architecture. Review time drops by 50-70% for experienced teams.
The simplest way to start:
# Get the diff of a PR or branch
git diff main...feature/your-branch > pr-diff.txt
# Start Claude Code and ask for a review
claude
# Then paste or reference the diff:
Review this diff for:
1. Bugs and logic errors
2. Security vulnerabilities (injection, auth bypass, data exposure)
3. Missing error handling
4. Null/undefined edge cases
5. Performance issues (N+1 queries, unnecessary re-renders, etc.)
Be specific. For each issue, tell me: what line, what the problem is, and how to fix it.These prompts are tuned for specific review goals. Save the ones that match your team's priorities.
Review this code for security vulnerabilities only. Focus on:
- SQL injection (unsanitized inputs in queries)
- XSS (unescaped user-controlled output in HTML)
- Authentication bypass (missing auth checks, insecure token handling)
- Authorization flaws (missing permission checks, IDOR patterns)
- Sensitive data exposure (logging secrets, returning more data than needed)
- Dependency vulnerabilities (outdated or suspicious package usage)
For each issue:
- Quote the exact line(s)
- Explain the attack vector (how would an attacker exploit this?)
- Provide the fixed version
If nothing is found, say so explicitly.Review this code for logic errors and edge cases. Check:
- What happens when inputs are null, undefined, empty string, or zero?
- What happens at array boundaries (empty array, single element, very large array)?
- What happens when async operations fail or timeout?
- Are there any off-by-one errors?
- Does every code path return a value / handle the case?
- Are there any race conditions if this runs concurrently?
For each issue: quote the line, describe the scenario that triggers it, and suggest a fix.Review this code for performance issues. Specifically look for:
- N+1 query patterns (database queries inside loops)
- Missing indexes implied by the query patterns
- Unnecessary re-renders (React: missing useMemo, useCallback, or key props)
- Memory leaks (event listeners not cleaned up, unclosed resources)
- Expensive operations that could be cached or memoized
- Synchronous operations that block when they could be async
- Large data structures loaded into memory when streaming would work
For each: identify the issue, estimate the impact (low/medium/high), and suggest the fix.Review this code and identify what tests are missing. For each function or code path:
1. What's the happy path test? Is it covered?
2. What are the error/failure paths? Are they covered?
3. What edge cases should be tested that aren't?
4. Are there any integration points (API calls, DB operations, external services) that need mocking?
List each missing test with: what to test, why it matters, and a brief code sketch of the test case.Do a complete code review of this diff. Structure your output as:
## Critical Issues (must fix before merge)
- Bug, security vulnerability, or data loss risk
- Quote the exact line(s), explain the issue, provide the fix
## Important Issues (should fix)
- Logic errors, missing error handling, performance problems
- Same format
## Suggestions (optional improvements)
- Code clarity, naming, DRY violations, test coverage gaps
- Brief note, not required to block merge
## What Looks Good
- 1-2 things done well (so the author knows what to keep doing)
Be direct and specific. Skip the generic commentary.If multiple engineers are using Claude Code for reviews, the CLAUDE.md file in your repo root is where you codify your team's standards. Claude reads it automatically on every run.
A good CLAUDE.md for code review includes:
# CLAUDE.md — Code Review Standards
## When reviewing code, always check:
### Security Non-Negotiables
- Every user input must be sanitized before DB operations
- All API endpoints require auth middleware unless explicitly marked `@public`
- Never log passwords, tokens, or PII — redact or hash first
- Environment variables must not be hardcoded — use process.env
### Error Handling Standards
- All async functions must have try/catch with specific error types
- HTTP errors must use our `AppError` class (see src/utils/errors.ts)
- Database errors must be caught and never surfaced to the client raw
### Patterns We Avoid
- No `any` types in TypeScript — use specific types or `unknown`
- No direct DOM manipulation in React — use state/refs
- No synchronous file I/O in request handlers
- No `.catch(console.log)` — errors must be logged with context
### Patterns We Prefer
- Functional components over class components
- Zod for runtime validation of external inputs
- Prisma transactions for multi-step DB operations
- Named exports over default exports
## Branch naming: feat/, fix/, chore/, docs/
## PR size: prefer under 400 lines changed per PR
## Tests required: unit tests for all business logic functionsClaude Code Hooks let you trigger reviews automatically at specific points in your workflow. The most useful: running a security scan before every git commit.
In your .claude/settings.json:
{
"hooks": {
"PreToolUse": [
{
"matcher": "Bash",
"hooks": [
{
"type": "command",
"command": "echo 'Running security pre-check...'",
"blocking": false
}
]
}
],
"PostToolUse": [
{
"matcher": "Write|Edit|MultiEdit",
"hooks": [
{
"type": "command",
"command": "echo 'File modified — review before committing.'",
"blocking": false
}
]
}
]
}
}For a more powerful pre-commit hook, add to your .git/hooks/pre-commit:
#!/bin/bash
# Run Claude Code security scan on staged files before commit
STAGED=$(git diff --cached --name-only --diff-filter=ACM | grep -E '\.(ts|js|py|go|rb)$')
if [ -z "$STAGED" ]; then
exit 0
fi
echo "Running Claude Code security scan on staged files..."
# Generate diff of staged changes only
DIFF=$(git diff --cached -- $STAGED)
# Quick security check (fast, non-interactive)
echo "$DIFF" | claude --print "Review this diff for ONLY critical security issues: SQL injection, auth bypass, hardcoded secrets, XSS. If none found, output PASS. If issues found, list them with line numbers." 2>/dev/null
exit 0--print flag runs Claude in non-interactive mode and outputs the result directly. This is fast enough for pre-commit hooks (typically 2-8 seconds for small diffs).
Not every PR needs the same depth. Match your review depth to the risk:
Use when: Small PRs, documentation changes, config updates, low-risk refactors.
Scan this diff for any obvious bugs or security issues. Two sentences max per issue. Skip anything that isn't critical.Use when: Feature additions, bug fixes, anything touching user data.
Use the "Full PR Review" prompt above. This is the default for most teams.
Use when: Authentication changes, payment flows, data exports, permission system changes.
This diff touches [auth/payments/data export]. Do a thorough security audit.
For each file changed:
1. What's the blast radius if this code is wrong? (what can an attacker do?)
2. Are there any auth or permission checks that could be bypassed?
3. Is sensitive data handled correctly throughout the flow?
4. Are there any race conditions or TOCTOU vulnerabilities?
I want you to think adversarially. Assume a motivated attacker will read this code. What do they exploit first?Knowing the limits is as important as knowing the strengths.
Claude Code will miss:
expect(result).toBe(5) when the correct answer is 4 will pass Claude's review unless it can independently verify the math.Here's how a 5-person engineering team might integrate Claude Code review:
Ready-to-use CLAUDE.md templates for 6 tech stacks (TypeScript, Python, React, Go, Java, PHP), a code review standards template, and a 20-prompt library for common review scenarios. Your team ships cleaner code from day one.
Get the Kit — $19 →