Code Review Skill | Agent Skills

Code Review

Comprehensive AI-powered code review for PRs and local changes — enterprise-grade alternative to CodeRabbit

When to use

"code review"
"review my PR"
"review PR #123"
"check my changes"
"what's wrong with my code"
"security review"
"full review"
"/review"
"/review-pr"

Dependencies

External: gh CLI (GitHub), git

Modes

1. Local review (uncommitted changes)

Reviews git diff — changes not yet committed.

2. Branch review (vs main/master)

Reviews all changes in current branch compared to main.

3. PR review (GitHub)

Fetches diff from GitHub PR and can post comments.

4. Focused review

User can request specific focus: security, performance, bugs, style, etc.

How to execute

Step 0: Check if review needed

Skip review if:

PR is draft (gh pr view --json isDraft)
PR is already closed/merged
Only documentation changes (.md, .txt, LICENSE)
Only config changes (.json, .yaml, .toml) without code impact
Trivial changes (<5 lines, whitespace only, version bumps)

Inform user and ask to confirm if they still want review.

Step 1: Determine mode

Ask user or detect automatically:

If PR number provided → PR review
If uncommitted changes exist → local review
If on feature branch → branch review
If specific focus requested → apply focus filter

Step 2: Get diff

Local:

git diff HEAD

Branch (vs main):

DEFAULT_BRANCH=$(git symbolic-ref refs/remotes/origin/HEAD 2>/dev/null | sed 's@^refs/remotes/origin/@@' || echo "main")
git diff $DEFAULT_BRANCH...HEAD

PR:

gh pr diff <PR_NUMBER>

Step 3: Get context

For thorough review, read related files:

# List changed files
git diff --name-only HEAD

# Read each file fully for context
# Check package.json for dependencies
# Check tsconfig/eslint config for project standards

Step 3b: Filter pre-existing issues

Before reporting an issue, check if it was introduced in this PR:

# Check when the problematic line was last modified
git blame -L <start>,<end> <file> --porcelain | head -1

Skip issues that:

Existed before this PR (old blame hash)
Are in unchanged lines
Were introduced by a different author long ago

Only report issues introduced or modified in current changes.

This prevents noise from legacy code and focuses review on new changes.

Step 4: Comprehensive Analysis

Apply ALL relevant checks from the checklist below.

Step 5: Confidence Scoring

Rate each issue 0-100:

| Score | Confidence | When to use | |-------|------------|-------------| | 90-100 | Certain | Clear vulnerability (SQL injection with user input), obvious crash | | 70-89 | High | Likely bug, security risk, definite code smell | | 50-69 | Medium | Potential issue, needs context to confirm | | 25-49 | Low | Style preference, minor suggestion | | 0-24 | Skip | Probably false positive, pre-existing, or nitpick |

Only report issues with confidence ≥70.

Mark as false positive and skip:

Pre-existing issues (caught by Step 3b)
Issues that linters will catch (eslint, prettier)
Pedantic nitpicks without real impact
Code that looks wrong but has valid reason (check comments)
Issues with explicit ignore comments (// eslint-disable, # noqa)

Step 6: Output result

Format:

## Code Review Summary

**Reviewed:** X files, Y lines changed
**Risk Level:** Critical / High / Medium / Low

### Critical Issues (must fix)
- [file:line] Description — Why it matters

### High Priority
- [file:line] Description

### Medium Priority
- [file:line] Description

### Low Priority / Suggestions
- [file:line] Description

### Good Practices
- What was done well

For GitHub PR — post comments:

# General comment on PR
gh pr comment <PR_NUMBER> --body "## AI Code Review
[Review content]"

# Line-by-line comments via API (for specific file/line feedback)
# Replace {owner}, {repo}, {pr} with actual values
gh api repos/{owner}/{repo}/pulls/{pr}/comments \
  --method POST \
  -f body="Issue description and fix suggestion" \
  -f path="src/file.ts" \
  -f line=42 \
  -f side="RIGHT"

COMPREHENSIVE REVIEW CHECKLIST

1. SECURITY (OWASP Top 10 + Extended)

1.1 Injection

[ ] SQL Injection — User input in SQL queries without parameterization
[ ] NoSQL Injection — Unsanitized input in MongoDB/similar queries
[ ] Command Injection — User input passed to shell commands (exec, spawn, system)
[ ] LDAP Injection — User input in LDAP queries
[ ] XPath Injection — User input in XML queries
[ ] Template Injection — User input in template engines (SSTI)
[ ] Header Injection — User input in HTTP headers (CRLF)
[ ] Log Injection — Unsanitized data written to logs

1.2 Broken Authentication

[ ] Weak password requirements — No complexity enforcement
[ ] Missing brute-force protection — No rate limiting on login
[ ] Session fixation — Session ID not regenerated after login
[ ] Insecure session storage — Sessions in localStorage (XSS vulnerable)
[ ] Missing logout — No session invalidation
[ ] Predictable tokens — Using weak random generators for tokens
[ ] Password in URL — Credentials in query parameters
[ ] Missing MFA on critical operations — No 2FA for sensitive actions

1.3 Sensitive Data Exposure

[ ] Hardcoded secrets — API keys, passwords, tokens in code
[ ] Secrets in logs — Sensitive data written to console/logs
[ ] Secrets in error messages — Stack traces exposing internals
[ ] Unencrypted sensitive data — PII/credentials not encrypted at rest
[ ] Weak cryptography — MD5, SHA1 for passwords, short keys
[ ] Missing HTTPS — HTTP links for sensitive operations
[ ] Sensitive data in URLs — Tokens/IDs in GET parameters
[ ] Excessive data exposure — Returning more fields than needed in API

1.4 XML External Entities (XXE)

[ ] XML parsing without disabling DTD — External entity processing enabled
[ ] Unsafe XML deserialization — User-controlled XML parsed

1.5 Broken Access Control

[ ] Missing authorization checks — Actions without permission verification
[ ] IDOR (Insecure Direct Object Reference) — Accessing resources by ID without ownership check
[ ] Privilege escalation — User can access admin functions
[ ] CORS misconfiguration — Wildcard or overly permissive origins
[ ] Missing function-level access control — API endpoints without role checks
[ ] Path traversal — User input in file paths (../)
[ ] Forced browsing — Unprotected admin/debug endpoints

1.6 Security Misconfiguration

[ ] Debug mode in production — Verbose errors, stack traces exposed
[ ] Default credentials — Unchanged default passwords
[ ] Unnecessary features enabled — Unused endpoints, methods
[ ] Missing security headers — No CSP, X-Frame-Options, etc.
[ ] Directory listing enabled — Exposed file structure
[ ] Outdated dependencies — Known vulnerabilities in packages
[ ] Permissive file permissions — World-readable sensitive files

1.7 Cross-Site Scripting (XSS)

[ ] Reflected XSS — User input echoed without encoding
[ ] Stored XSS — Database content rendered without sanitization
[ ] DOM XSS — Client-side JS using unsafe sinks (innerHTML, eval)
[ ] Missing Content-Security-Policy — No CSP headers
[ ] Unsafe React patterns — dangerouslySetInnerHTML with user content
[ ] Template literal injection — User input in template strings

1.8 Insecure Deserialization

[ ] Unsafe JSON parsing — eval() for JSON
[ ] Object deserialization — pickle, serialize without validation
[ ] Prototype pollution — Object.assign/merge with user input

1.9 Using Components with Known Vulnerabilities

[ ] Outdated dependencies — Check package.json against vulnerability databases
[ ] Abandoned packages — Dependencies with no recent updates
[ ] Typosquatting — Suspicious package names

1.10 Insufficient Logging & Monitoring

[ ] Missing audit logs — No logging for security events
[ ] Missing error handling — Silent failures
[ ] No alerting — Security events not monitored

1.11 Additional Security Checks

[ ] SSRF (Server-Side Request Forgery) — User-controlled URLs in server requests
[ ] Open Redirect — User input in redirect URLs
[ ] CSRF protection missing — No tokens for state-changing operations
[ ] JWT issues — Weak secret, algorithm confusion, no expiry
[ ] Regex DoS (ReDoS) — Catastrophic backtracking in regex
[ ] Mass assignment — Binding request body directly to models
[ ] File upload vulnerabilities — No type validation, path traversal
[ ] Race conditions — TOCTOU (time-of-check-time-of-use) issues

2. BUGS & LOGIC ERRORS

2.1 Null/Undefined Handling

[ ] Null pointer dereference — Accessing properties of null/undefined
[ ] Missing null checks — Optional chaining not used where needed
[ ] Null coalescing issues — Wrong default values
[ ] Falsy value confusion — 0, '', false treated as null

2.2 Type Issues

[ ] Type coercion bugs — == instead of ===
[ ] Implicit type conversion — String + Number concatenation
[ ] Missing type checks — typeof/instanceof not used
[ ] Type assertion abuse — Unsafe 'as' casts in TypeScript
[ ] Any type overuse — Losing type safety

2.3 Async/Concurrency

[ ] Missing await — Unhandled promises
[ ] Unhandled promise rejection — No .catch() or try/catch
[ ] Race conditions — Shared state without synchronization
[ ] Deadlocks — Circular waiting for resources
[ ] Callback hell — Nested callbacks instead of async/await
[ ] Memory leaks from listeners — Event listeners not removed
[ ] Stale closures — Capturing old values in closures

2.4 Loop/Iteration Errors

[ ] Off-by-one errors — Wrong loop bounds
[ ] Infinite loops — Missing break condition
[ ] Mutating while iterating — Modifying collection during loop
[ ] Wrong loop variable — Using outer variable in nested loop
[ ] forEach with async — Not waiting for async operations

2.5 Boundary/Edge Cases

[ ] Empty array/object — Not handling empty collections
[ ] Single element — Edge case for arrays with one item
[ ] Negative numbers — Not handling negative input
[ ] Zero division — Dividing without checking denominator
[ ] Integer overflow — Large number calculations
[ ] Floating point precision — 0.1 + 0.2 !== 0.3
[ ] Unicode/encoding — Special characters not handled
[ ] Timezone issues — Date handling without timezone awareness
[ ] Daylight saving time — Date calculations across DST

2.6 State Management

[ ] Stale state — React setState with stale closure
[ ] Missing state updates — UI not reflecting state
[ ] State mutation — Direct state modification
[ ] Prop drilling issues — Props passed too deep
[ ] Unnecessary re-renders — Missing memoization

2.7 Error Handling

[ ] Empty catch blocks — Swallowing errors silently
[ ] Generic error handling — Catching all without specificity
[ ] Missing finally — Resources not cleaned up
[ ] Rethrowing without context — Losing stack trace
[ ] Error in error handler — Handler itself can throw

2.8 Resource Management

[ ] Resource leaks — Files, connections not closed
[ ] Memory leaks — Objects not garbage collected
[ ] Connection pool exhaustion — Not returning connections
[ ] File handle leaks — Streams not closed
[ ] Timer leaks — setInterval not cleared

2.9 Business Logic

[ ] Wrong calculations — Incorrect formulas
[ ] Missing validation — Business rules not enforced
[ ] State machine violations — Invalid state transitions
[ ] Duplicate operations — Same action performed twice
[ ] Missing rollback — Partial updates on failure

3. PERFORMANCE

3.1 Database

[ ] N+1 queries — Loop with individual queries
[ ] Missing indexes — Queries on unindexed columns
[ ] **SELECT *** — Fetching unnecessary columns
[ ] Missing pagination — Loading all records
[ ] Missing connection pooling — New connection per request
[ ] Expensive JOINs — Large table joins without optimization
[ ] Missing query caching — Repeated identical queries
[ ] Transaction scope too large — Holding locks too long
[ ] Inefficient aggregations — COUNT/SUM without indexes

3.2 API/Network

[ ] Missing caching — No Cache-Control headers
[ ] Over-fetching — Returning more data than needed
[ ] Under-fetching — Multiple requests for related data
[ ] No compression — Missing gzip/brotli
[ ] Chatty APIs — Too many small requests
[ ] Missing pagination — Large response payloads
[ ] Synchronous external calls — Blocking on I/O
[ ] Missing timeouts — No timeout on HTTP calls
[ ] Missing retry logic — No retry for transient failures

3.3 Frontend

[ ] Large bundle size — Missing code splitting
[ ] Render blocking resources — CSS/JS blocking paint
[ ] Unnecessary re-renders — Missing React.memo, useMemo
[ ] Large images — Unoptimized images
[ ] Missing lazy loading — Loading offscreen content
[ ] Layout thrashing — Forced synchronous layouts
[ ] Heavy animations — Expensive CSS/JS animations
[ ] Memory leaks — Detached DOM nodes
[ ] Long tasks — Blocking main thread >50ms

3.4 Algorithms

[ ] O(n²) or worse — Nested loops on large data
[ ] Repeated calculations — No memoization
[ ] String concatenation in loops — Using += for strings
[ ] Inefficient data structures — Array instead of Set/Map
[ ] Unnecessary copying — Deep clone when not needed
[ ] Redundant sorting — Sorting already sorted data

3.5 Caching

[ ] Missing caching layer — No Redis/Memcached
[ ] Cache invalidation issues — Stale data served
[ ] Cache stampede — Many requests on cache miss
[ ] No cache warming — Cold start performance
[ ] Unbounded cache — No eviction policy

4. CODE QUALITY

4.1 Readability

[ ] Poor naming — Unclear variable/function names
[ ] Magic numbers — Hardcoded values without constants
[ ] Long functions — Functions >50 lines
[ ] Deep nesting — >3 levels of indentation
[ ] Complex conditionals — Hard to understand if/else chains
[ ] Missing comments for complex logic — Unclear algorithms
[ ] Inconsistent naming convention — camelCase mixed with snake_case
[ ] Abbreviations — Unclear shortened names

4.2 Maintainability

[ ] DRY violations — Copy-pasted code
[ ] God objects/functions — Doing too much
[ ] Tight coupling — Hard dependencies between modules
[ ] Missing abstraction — Repeated patterns not extracted
[ ] Premature abstraction — Over-engineering simple code
[ ] Circular dependencies — Modules importing each other
[ ] Dead code — Unused functions, variables, imports
[ ] Commented-out code — Old code left in comments
[ ] TODO/FIXME/HACK — Technical debt markers

4.3 SOLID Principles

[ ] Single Responsibility — Class/function doing multiple things
[ ] Open/Closed — Modifying instead of extending
[ ] Liskov Substitution — Subclasses breaking parent contract
[ ] Interface Segregation — Fat interfaces
[ ] Dependency Inversion — Depending on concretions

4.4 Error Messages

[ ] Generic error messages — "Something went wrong"
[ ] Technical jargon for users — Stack traces shown to users
[ ] Missing error codes — No way to identify errors
[ ] Non-actionable errors — User doesn't know what to do

4.5 API Design

[ ] Inconsistent response format — Different structures per endpoint
[ ] Wrong HTTP methods — POST for GET operations
[ ] Wrong status codes — 200 for errors
[ ] Missing versioning — No API version in path/header
[ ] Breaking changes — Removing/renaming fields
[ ] Missing documentation — No OpenAPI/Swagger

4.6 Configuration

[ ] Hardcoded configuration — No environment variables
[ ] Missing defaults — Required config without fallback
[ ] Scattered config — Configuration in multiple places
[ ] Secrets in config files — Credentials in committed files

5. TESTING

5.1 Test Coverage

[ ] Missing unit tests — Critical functions untested
[ ] Missing integration tests — API endpoints untested
[ ] Missing edge case tests — Only happy path tested
[ ] Missing error case tests — Error handling untested
[ ] Low coverage on changed files — New code not tested

5.2 Test Quality

[ ] Flaky tests — Tests that sometimes fail
[ ] Slow tests — Tests taking too long
[ ] Test interdependence — Tests depending on order
[ ] Missing assertions — Tests without expect/assert
[ ] Testing implementation — Testing how, not what
[ ] Mocking too much — Testing mocks, not code
[ ] Missing test data cleanup — Side effects between tests

5.3 Test Patterns

[ ] Missing describe blocks — No test organization
[ ] Unclear test names — "test1", "should work"
[ ] Arrange-Act-Assert — Unclear test structure
[ ] Missing fixtures — Repeated test data setup

6. ACCESSIBILITY (a11y)

[ ] Missing alt text — Images without alt attributes
[ ] Missing form labels — Inputs without labels
[ ] Color contrast — Insufficient contrast ratio
[ ] Keyboard navigation — Not usable without mouse
[ ] Missing ARIA labels — Interactive elements without labels
[ ] Focus management — Focus not handled in modals/SPAs
[ ] Missing skip links — No way to skip navigation
[ ] Missing heading hierarchy — Improper h1-h6 usage
[ ] Auto-playing media — No way to stop audio/video
[ ] Missing screen reader text — Icons without labels

7. INTERNATIONALIZATION (i18n)

[ ] Hardcoded strings — Text not in translation files
[ ] Date/time formatting — Not using locale-aware formatting
[ ] Number formatting — Not handling decimal separators
[ ] Currency formatting — Not handling currency symbols
[ ] RTL support — Not handling right-to-left languages
[ ] Pluralization — Not handling singular/plural
[ ] String concatenation — Building sentences from parts
[ ] Hardcoded date formats — MM/DD/YYYY vs DD/MM/YYYY

8. DOCUMENTATION

[ ] Missing README — No project documentation
[ ] Outdated documentation — Docs don't match code
[ ] Missing API docs — No endpoint documentation
[ ] Missing JSDoc/TSDoc — Public APIs undocumented
[ ] Missing changelog — No record of changes
[ ] Missing setup instructions — Hard to get started
[ ] Broken links — Dead URLs in README, docs, or code comments
[ ] Relative link errors — Wrong paths to internal docs/files

9. DEVOPS / INFRASTRUCTURE

[ ] Missing health checks — No /health endpoint
[ ] Missing graceful shutdown — Not handling SIGTERM
[ ] Missing retry logic — No resilience patterns
[ ] Missing circuit breaker — No failure isolation
[ ] Logging not structured — Plain text instead of JSON
[ ] Missing correlation IDs — Can't trace requests
[ ] Missing metrics — No observability
[ ] Missing alerts — No monitoring
[ ] Container issues — Running as root, large images
[ ] Missing resource limits — No CPU/memory limits

10. GIT/VERSION CONTROL

[ ] Large files committed — Binary files, node_modules
[ ] Secrets in history — API keys in past commits
[ ] Merge conflicts markers — Unresolved conflicts
[ ] Mixed line endings — CRLF/LF issues
[ ] Missing .gitignore entries — Temporary files tracked
[ ] Large commits — Too many changes in one commit
[ ] Unclear commit messages — "fix", "update", "wip"

LANGUAGE-SPECIFIC CHECKS (apply if relevant files detected)

11. REACT / NEXT.JS (if .tsx, .jsx files)

[ ] useEffect missing deps — Dependencies array incomplete or missing
[ ] useEffect cleanup — Missing cleanup for subscriptions, timers
[ ] useState stale closure — Using state in callbacks without functional update
[ ] Key prop issues — Missing key, using index as key in dynamic lists
[ ] useMemo/useCallback overuse — Premature optimization
[ ] Prop drilling — Props passed through many levels (use context)
[ ] Component too large — >300 lines, should be split
[ ] Inline function in JSX — Creating new function on every render
[ ] Direct DOM manipulation — Using document.querySelector in React
[ ] Missing error boundary — No error handling for component tree

12. TYPESCRIPT (if .ts, .tsx files)

[ ] Any type abuse — Using any to bypass type checking
[ ] Type assertion abuse — Unsafe as casts without validation
[ ] Missing return types — Public functions without explicit return type
[ ] Implicit any — Variables without type annotation
[ ] Non-null assertion — Overuse of ! operator
[ ] Enum vs union — Using enum where union type is better
[ ] Unused exports — Exported types/functions never imported

13. PYTHON (if .py files)

[ ] Mutable default args — def foo(items=[]) anti-pattern
[ ] Missing type hints — Public functions without annotations
[ ] Bare except — except: without specific exception
[ ] Context manager — File/connection not using with
[ ] Global state — Modifying global variables
[ ] Import side effects — Code execution at import time
[ ] f-string security — User input in f-strings (potential injection)

14. NODE.JS / EXPRESS (if package.json with express)

[ ] Async error handling — Missing try/catch in async routes
[ ] Missing helmet — No security headers middleware
[ ] Missing rate limiting — No protection against abuse
[ ] Callback hell — Nested callbacks instead of async/await
[ ] Blocking event loop — Sync operations in request handlers
[ ] Missing input validation — No validation middleware (joi, zod)
[ ] Hardcoded CORS — Wildcard or hardcoded origins

15. SQL / DATABASE (if .sql files or ORM usage)

[ ] Raw queries — String concatenation instead of parameterized
[ ] Missing indexes — Queries on frequently filtered columns
[ ] N+1 in ORM — Lazy loading in loops
[ ] Wide transactions — Transaction scope too large
[ ] Missing migrations — Schema changes without migration files
[ ] Cascading deletes — Unintended data loss on delete

Parameters

| Parameter | Description | Default | |-----------|-------------|---------| | PR_NUMBER | Pull Request number | - | | --post | Post comments to GitHub | false | | --severity | Minimum level (critical/high/medium/low) | low | | --focus | Focus area: security, performance, bugs, quality, testing, a11y, i18n, all | all |

Examples

Example 1: Full review

User: full code review

Claude: [git diff HEAD]
Claude: [comprehensive analysis using all checklists]
Claude:
## Code Review Summary

**Reviewed:** 5 files, 234 lines changed
**Risk Level:** High

### Critical Issues (2)
1. [src/api/auth.ts:45] SQL Injection - User input passed directly to query
2. [src/utils/crypto.ts:12] Weak cryptography - Using MD5 for password hashing

### High Priority (3)
1. [src/services/user.ts:78] Missing authorization check - IDOR vulnerability
2. [src/api/data.ts:23] N+1 query - 50 queries in loop
3. [src/components/Form.tsx:156] XSS - dangerouslySetInnerHTML with user content

### Medium Priority (5)
...

Example 2: Security-focused review

User: security review PR 123

Claude: [applies only security checklist]
Claude: Found 3 security issues...

Example 3: Performance review

User: check performance issues in my changes

Claude: [applies only performance checklist]
Claude: Found 2 performance issues...

Severity Levels

| Level | Description | Examples | |-------|-------------|----------| | Critical | Must fix before merge. Security vulnerabilities, data loss risks | SQL injection, hardcoded secrets, auth bypass | | High | Should fix before merge. Significant bugs or security issues | N+1 queries, XSS, missing error handling | | Medium | Fix soon. Code quality, minor bugs | DRY violations, missing tests, complexity | | Low | Nice to have. Suggestions, style | Naming, comments, minor optimizations |

Troubleshooting

| Problem | Solution | |---------|----------| | gh: command not found | brew install gh && gh auth login | | No diff output | Check if changes exist: git status | | PR not found | Check PR number and access rights | | Can't post comments | Check permissions: gh auth status | | Review too long | Use --focus to narrow scope | | False positives | Mention specific context to skip |

Limitations

Static analysis only — cannot run code
Cannot see runtime behavior
May miss complex cross-file issues
Needs context for architectural decisions
GitHub API rate limits when posting many comments
Language-specific checks may vary in depth

If you're getting false positives

Step 1: Use severity filter

Most false positives are low/medium severity. Start with high-only:

"review PR 123 --severity=high"
"review my changes, only critical and high issues"

Step 2: Use focus filter

Narrow to specific categories you care about:

"security review PR 123"
"review PR 123 --focus=bugs,security"
"check only performance issues"

Step 3: Tell Claude to skip specific issues

In the same conversation, provide context:

"ignore the N+1 warning in admin routes - it's intentional, low traffic"
"skip any type warnings in src/legacy/ - that's legacy code"
"the raw SQL in migrations/ is fine, we use raw migrations"

Step 4: Add inline comment in code

For persistent false positives that keep appearing:

// @review-ok: parameterized query handled by ORM
const query = `SELECT * FROM users WHERE id = ${sanitizedId}`;

# @review-ok: global cache intentional for performance
CACHE = {}

Step 5: Report to improve the skill

If the same false positive keeps appearing across reviews:

Open issue at github.com/your-org/claude-code-review-skill/issues
Include:
- File and line number
- What was flagged
- Why it's a false positive
- Code snippet if possible

This helps improve the skill for everyone.

Default behavior

The skill is designed to minimize false positives out of the box:

Baseline filtering — Only reports issues introduced in current PR/changes (via git blame)
Confidence threshold — Only reports issues with ≥70% confidence
Skips linter territory — Doesn't flag formatting, style issues that ESLint/Prettier catch
Skips pre-existing issues — Won't complain about old code you didn't touch
Skips trivial changes — Version bumps, whitespace, documentation-only changes

Agent Skills: Code Review

Install this agent skill to your local

Skill Files