OpenAI Codex Code Review Skill

# OpenAI Codex Code Review Skill


Use OpenAI's Codex CLI for specialized code review with GPT-5.2-Codex - trained specifically for detecting bugs, security flaws, and code quality issues.

**Sources:** [Codex CLI](https://developers.openai.com/codex/cli/) | [GitHub](https://github.com/openai/codex) | [Code Review Cookbook](https://cookbook.openai.com/examples/codex/build_code_review_with_codex_sdk)

---

## Why Codex for Code Review?

| Feature | Benefit |
|---------|---------|
| **GPT-5.2-Codex** | Specialized training for code review |
| **88% detection rate** | Bugs, security flaws, style issues (LiveCodeBench) |
| **Structured output** | JSON schema for consistent findings |
| **GitHub native** | `@codex review` in PR comments |
| **Headless mode** | CI/CD automation without TUI |

---

## Installation

### Prerequisites

```bash
# Check Node.js version (requires 22+)
node --version

# Install Node.js 22 if needed
# macOS
brew install node@22

# Or via nvm
nvm install 22
nvm use 22
```

### Install Codex CLI

```bash
# Via npm (recommended)
npm install -g @openai/codex

# Via Homebrew (macOS)
brew install --cask codex

# Verify installation
codex --version
```

### Authentication

**Option 1: ChatGPT Subscription** (Plus, Pro, Team, Edu, Enterprise)
```bash
codex
# Follow prompts to sign in with ChatGPT account
```

**Option 2: OpenAI API Key**
```bash
# Set environment variable
export OPENAI_API_KEY=sk-proj-...

# Or add to shell profile
echo 'export OPENAI_API_KEY=sk-proj-...' >> ~/.zshrc

# Run Codex
codex
```

### Shell Completions (Optional)

```bash
# Bash
codex completion bash >> ~/.bashrc

# Zsh
codex completion zsh >> ~/.zshrc

# Fish
codex completion fish > ~/.config/fish/completions/codex.fish
```

---

## Interactive Code Review

### Launch Review Mode

```bash
# Start Codex
codex

# In the TUI, type:
/review
```

### Review Presets

| Preset | Use Case |
|--------|----------|
| **Review against base branch** | Before opening PR - diffs against upstream |
| **Review uncommitted changes** | Before committing - staged + unstaged + untracked |
| **Review a commit** | Analyze specific SHA from history |
| **Custom instructions** | e.g., "Focus on security vulnerabilities" |

### Example Session

```
$ codex
> /review

Select review type:
❯ Review against a base branch
  Review uncommitted changes
  Review a commit
  Custom review instructions

Select base branch: main

Reviewing changes...

┌─────────────────────────────────────────────────────────────┐
│ CODE REVIEW FINDINGS                                        │
├─────────────────────────────────────────────────────────────┤
│ 🔴 CRITICAL: SQL Injection vulnerability                    │
│    File: src/api/users.ts:45                                │
│    Issue: User input directly interpolated in query         │
│    Fix: Use parameterized queries                           │
├─────────────────────────────────────────────────────────────┤
│ 🟠 HIGH: Missing authentication check                       │
│    File: src/api/admin.ts:23                                │
│    Issue: Admin endpoint accessible without auth            │
│    Fix: Add requireAuth middleware                          │
├─────────────────────────────────────────────────────────────┤
│ 🟡 MEDIUM: Inefficient database query                       │
│    File: src/services/orders.ts:89                          │
│    Issue: N+1 query pattern in loop                         │
│    Fix: Use batch query or JOIN                             │
└─────────────────────────────────────────────────────────────┘
```

---

## Headless Mode (Automation)

### Basic Usage

```bash
# Simple review
codex exec "review the code for bugs and security issues"

# Review with JSON output
codex exec --json "review uncommitted changes" > review.json

# Save final message to file
codex exec --output-last-message review.txt "review the diff against main"
```

### Full Automation (CI/CD)

```bash
# Full auto mode (use only in isolated runners!)
codex exec \
  --full-auto \
  --json \
  --output-last-message findings.txt \
  --sandbox read-only \
  -m gpt-5.2-codex \
  "Review this code for bugs, security issues, and performance problems"
```

### Structured Output with Schema

```bash
# Define output schema
cat > review-schema.json << 'EOF'
{
  "type": "object",
  "properties": {
    "findings": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "severity": { "enum": ["critical", "high", "medium", "low"] },
          "title": { "type": "string" },
          "file": { "type": "string" },
          "line": { "type": "integer" },
          "description": { "type": "string" },
          "suggestion": { "type": "string" }
        },
        "required": ["severity", "title", "file", "description"]
      }
    },
    "summary": { "type": "string" },
    "approved": { "type": "boolean" }
  },
  "required": ["findings", "summary", "approved"]
}
EOF

# Run with schema validation
codex exec \
  --output-schema review-schema.json \
  --output-last-message review.json \
  "Review the staged changes and output findings"
```

---

## GitHub Integration

### Option 1: PR Comment Trigger

In any pull request, add a comment:
```
@codex review
```

Codex will respond with a standard GitHub code review.

### Option 2: GitHub Action

```yaml
# .github/workflows/codex-review.yml
name: Codex Code Review

on:
  pull_request:
    types: [opened, synchronize]

jobs:
  review:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write

    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Codex Review
        uses: openai/codex-action@main
        with:
          openai_api_key: ${{ secrets.OPENAI_API_KEY }}
          model: gpt-5.2-codex
          safety_strategy: drop-sudo
```

### Option 3: Manual Headless in CI

```yaml
# .github/workflows/codex-review.yml
name: Codex Code Review

on:
  pull_request:

jobs:
  review:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - uses: actions/setup-node@v4
        with:
          node-version: '22'

      - name: Install Codex CLI
        run: npm install -g @openai/codex

      - name: Run Review
        env:
          OPENAI_API_KEY: ${{ secrets.OPENAI_API_KEY }}
        run: |
          # Get diff
          git diff origin/${{ github.base_ref }}...HEAD > diff.txt

          # Run Codex review
          codex exec \
            --full-auto \
            --sandbox read-only \
            --output-last-message review.md \
            "Review this git diff for bugs, security issues, and code quality: $(cat diff.txt)"

      - name: Post Review Comment
        uses: actions/github-script@v7
        with:
          script: |
            const fs = require('fs');
            const review = fs.readFileSync('review.md', 'utf8');
            github.rest.issues.createComment({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: context.issue.number,
              body: `## 🤖 Codex Code Review\n\n${review}`
            });
```

---

## GitLab CI/CD

```yaml
# .gitlab-ci.yml
codex-review:
  image: node:22
  stage: review
  script:
    - npm install -g @openai/codex
    - |
      codex exec \
        --full-auto \
        --sandbox read-only \
        --output-last-message review.md \
        "Review the merge request changes for bugs and security issues"
    - cat review.md
  artifacts:
    paths:
      - review.md
  rules:
    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
```

---

## Jenkins Pipeline

```groovy
pipeline {
    agent any

    environment {
        OPENAI_API_KEY = credentials('openai-api-key')
    }

    stages {
        stage('Install Codex') {
            steps {
                sh 'npm install -g @openai/codex'
            }
        }

        stage('Code Review') {
            steps {
                sh '''
                    codex exec \
                      --full-auto \
                      --sandbox read-only \
                      --output-last-message review.md \
                      "Review the code changes for bugs and security issues"
                '''
            }
        }

        stage('Publish Results') {
            steps {
                archiveArtifacts artifacts: 'review.md'
                script {
                    def review = readFile('review.md')
                    echo "Code Review Results:\n${review}"
                }
            }
        }
    }
}
```

---

## Configuration

### Config File

```toml
# ~/.codex/config.toml

[model]
default = "gpt-5.2-codex"  # Best for code review

[sandbox]
default = "read-only"  # Safe for reviews

[review]
# Custom review instructions applied to all reviews
instructions = """
Focus on:
1. Security vulnerabilities (OWASP Top 10)
2. Performance issues (N+1 queries, memory leaks)
3. Error handling gaps
4. Type safety issues
"""
```

### Per-Project Config

```toml
# .codex/config.toml (in project root)

[review]
instructions = """
This is a Python FastAPI project. Focus on:
- Async/await correctness
- Pydantic model validation
- SQL injection via SQLAlchemy
- Authentication/authorization gaps
"""
```

---

## CLI Quick Reference

```bash
# Interactive
codex                          # Start TUI
/review                        # Open review presets

# Headless
codex exec "prompt"            # Non-interactive execution
codex exec --json "prompt"     # JSON output
codex exec --full-auto "prompt"  # No approval prompts

# Key Flags
--output-last-message FILE     # Save response to file
--output-schema FILE           # Validate against JSON schema
--sandbox read-only            # Restrict file access
-m gpt-5.2-codex              # Use best review model
--json                         # Machine-readable output

# Resume
codex exec resume SESSION_ID   # Continue previous session
```

---

## Comparison: Claude vs Codex Review

| Aspect | Claude (Built-in) | Codex CLI |
|--------|-------------------|-----------|
| **Setup** | None (already in Claude Code) | Install CLI + auth |
| **Model** | Claude | GPT-5.2-Codex (specialized) |
| **Context** | Full conversation context | Fresh context per review |
| **Integration** | Native | GitHub, GitLab, Jenkins |
| **Output** | Markdown | JSON schema support |
| **Best for** | Quick reviews, in-flow | CI/CD, critical PRs |

---

## Security Considerations

### CI/CD Safety

```yaml
# Always use these flags in CI/CD:
--sandbox read-only           # Prevent file modifications
--safety-strategy drop-sudo   # Revoke elevated permissions
```

### API Key Protection

```yaml
# GitHub Actions - use secrets
env:
  OPENAI_API_KEY: ${{ secrets.OPENAI_API_KEY }}

# Never hardcode keys
# Never echo keys in logs
```

### Public Repositories

For public repos, use `drop-sudo` safety strategy to prevent Codex from reading its own API key during execution.

---

## Troubleshooting

| Issue | Solution |
|-------|----------|
| `codex: command not found` | Run `npm install -g @openai/codex` |
| `Node.js version error` | Upgrade to Node.js 22+ |
| `Authentication failed` | Re-run `codex` and sign in again |
| `API key invalid` | Check `OPENAI_API_KEY` env var |
| `Timeout in CI` | Add `--timeout 300` flag |
| `Rate limited` | Reduce frequency or upgrade plan |

---

## Anti-Patterns

- **Using `--dangerously-bypass-approvals-and-sandbox` casually** - Only in isolated CI runners
- **Exposing API keys in logs** - Use secrets management
- **Skipping sandbox in CI** - Always use `--sandbox read-only`
- **Ignoring findings** - Review and address or document exceptions
- **Running on every commit** - Use on PRs only to save costs