Code Reviewer

Code Reviewer

Review code systematically for bugs, security issues, and quality problems.

When to Use

• Before merging a pull request
• After finishing a feature (self-review)
• Auditing code for security or compliance
• Onboarding to an unfamiliar codebase
• Before deploying to production

How It Works

1. Review Checklist

Go through these categories in order:

Priority 1 — Security
├── SQL injection (raw queries, string concatenation)
├── XSS (unescaped user input in HTML/JSX)
├── Auth bypass (missing middleware, broken checks)
├── Secrets in code (API keys, passwords, tokens)
├── Insecure dependencies (known CVEs)
└── CSRF / CORS misconfiguration

Priority 2 — Correctness
├── Logic errors (off-by-one, wrong operator, inverted condition)
├── Null/undefined access without checks
├── Race conditions (async operations, shared state)
├── Error handling (uncaught exceptions, silent failures)
├── Edge cases (empty arrays, zero values, large inputs)
└── Type safety (any casts, missing types)

Priority 3 — Performance
├── N+1 queries (loop with DB call inside)
├── Missing pagination on list endpoints
├── Unnecessary re-renders (React)
├── Large bundle imports (import entire library for one function)
├── Missing indexes on queried columns
└── Memory leaks (uncleared intervals, listeners, subscriptions)

Priority 4 — Maintainability
├── Function length (> 30 lines = too long)
├── Naming clarity (can you understand it without context?)
├── Duplication (same logic in 2+ places)
├── Dead code (unused imports, unreachable branches)
├── Missing tests for new logic
└── Consistent patterns with rest of codebase

2. Security Deep Dive

SQL Injection:

// BAD — string interpolation
const users = await db.query(`SELECT * FROM users WHERE name = '${name}'`)

// GOOD — parameterized query
const users = await db.query('SELECT * FROM users WHERE name = $1', [name])

// GOOD — ORM (Prisma)
const users = await db.user.findMany({ where: { name } })

XSS:

// BAD — renders raw HTML from user input
<div dangerouslySetInnerHTML={{ __html: userComment }} />

// GOOD — React auto-escapes by default
<div>{userComment}</div>

// If HTML is needed — sanitize first
import DOMPurify from 'dompurify'
<div dangerouslySetInnerHTML={{ __html: DOMPurify.sanitize(userComment) }} />

Auth Checks:

// BAD — no auth on sensitive endpoint
export async function DELETE(req: Request, { params }: { params: { id: string } }) {
  await db.user.delete({ where: { id: params.id } })
  return NextResponse.json({ ok: true })
}

// GOOD — verify authentication and authorization
export async function DELETE(req: Request, { params }: { params: { id: string } }) {
  const session = await getServerSession()
  if (!session) return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
  if (session.user.id !== params.id && session.user.role !== 'admin') {
    return NextResponse.json({ error: 'Forbidden' }, { status: 403 })
  }
  await db.user.delete({ where: { id: params.id } })
  return NextResponse.json({ ok: true })
}

3. Performance Checks

N+1 Query:

// BAD — N+1: one query per post to get author
const posts = await db.post.findMany()
for (const post of posts) {
  post.author = await db.user.findUnique({ where: { id: post.authorId } })
}

// GOOD — single query with include
const posts = await db.post.findMany({
  include: { author: { select: { name: true, email: true } } }
})

React Re-renders:

// BAD — new object on every render triggers child re-render
<UserCard style={{ padding: 16 }} />

// GOOD — stable reference
const cardStyle = { padding: 16 } // outside component
// or
const cardStyle = useMemo(() => ({ padding: 16 }), [])

4. Review Output Format

For each issue found:

### [SEVERITY] Issue title

**File:** `src/api/users/route.ts:24`
**Category:** Security / Correctness / Performance / Maintainability

**Problem:** Description of what's wrong and why it matters.

**Fix:**
\`\`\`typescript
// suggested fix
\`\`\`

Severity levels:

• CRITICAL — Must fix before merge (security vulnerability, data loss)
• WARNING — Should fix (bug risk, performance issue)
• INFO — Consider improving (readability, convention)

5. Quick Commands

# Check for known vulnerabilities in dependencies
npm audit

# Find TODO/FIXME/HACK comments
grep -rn "TODO\|FIXME\|HACK" src/

# Check TypeScript errors
npx tsc --noEmit

# Run linter
npx eslint src/

# Check for unused exports
npx knip

Quality Checklist

• No hardcoded secrets or API keys
• All user input is validated/sanitized
• Auth checks on every protected endpoint
• No N+1 queries
• Error states handled (try/catch, error boundaries)
• Tests cover the new/changed code
• No console.log left in production code

Examples

> Review all uncommitted changes for security issues
> Do a full code review of the /api directory
> Check this PR for performance problems