Codex Advisor

Overview

Use OpenAI's Codex CLI as a second-opinion advisor when you need external validation on plans, code reviews, or are stuck on hard problems. This skill uses non-interactive mode (codex exec) for scripted/automated usage.

When to Use

• Reviewing implementation plans before starting work
• Code review for complex or security-sensitive changes
• Architecture decisions with significant trade-offs
• Debugging problems where you've been stuck for >30 minutes
• Getting alternative approaches to a solution
• Validating assumptions about unfamiliar codebases

Prerequisites

• OpenAI API key or ChatGPT Plus/Pro/Business account
• Codex CLI installed

Installation

# Via npm
npm install -g @openai/codex

# Or via Homebrew
brew install --cask codex

Authentication

# Option 1: API key (required for non-interactive mode in CI)
export OPENAI_API_KEY="your-key"

# Option 2: Codex-specific key for CI environments
export CODEX_API_KEY="your-key"

# Option 3: Interactive login (one-time setup)
codex --login

Model Selection

Choose the right model for your task:

Recommendation:

• Start with gpt-5.2 for general questions
• Use gpt-5.2-codex when the task is specifically about code
• Use gpt-5.1-codex-max for tasks involving many files or complex multi-step work

Reasoning Effort Levels

Always use xhigh reasoning for thorough analysis:

Non-Interactive Mode

All commands use codex exec for non-interactive execution. This is essential for scripted usage and piping.

Key Flags

Output Handling

# JSON output for parsing
codex exec -m gpt-5.2 -c model_reasoning_effort="xhigh" \
  --json "Your prompt" 2>/dev/null

# Save to file
codex exec -m gpt-5.2 -c model_reasoning_effort="xhigh" \
  -o output.txt "Your prompt"

# Pipe input and capture output
git diff | codex exec -m gpt-5.2-codex -c model_reasoning_effort="xhigh" \
  "Review this diff" > review.txt 2>/dev/null

Command Reference

Plan Review

Get feedback on an implementation plan:

codex exec -m gpt-5.2 -c model_reasoning_effort="xhigh" \
  "Review this implementation plan. Identify potential issues, missing edge cases, security concerns, or better approaches:

<paste plan here>"

For plans involving the current codebase:

codex exec -m gpt-5.2 -c model_reasoning_effort="xhigh" -C . \
  "Review this implementation plan in the context of this codebase. Identify potential issues, conflicts with existing patterns, or better approaches:

<paste plan here>"

Code Review

Review code changes for bugs, security issues, and improvements:

# Review staged changes
git diff --staged | codex exec -m gpt-5.2-codex -c model_reasoning_effort="xhigh" \
  "Review these changes before commit. Check for:
- Bugs or logic errors
- Security vulnerabilities
- Performance issues
- Missing error handling"

# Review a specific diff
git diff | codex exec -m gpt-5.2-codex -c model_reasoning_effort="xhigh" \
  "Review this diff for bugs, security issues, and improvements"

# Review with codebase context
codex exec -m gpt-5.2-codex -c model_reasoning_effort="xhigh" -C . \
  "Review src/auth/login.ts for bugs, security vulnerabilities, and suggest improvements"

Hard Problem Solving

When stuck on a difficult problem:

codex exec -m gpt-5.2-codex -c model_reasoning_effort="xhigh" -C . \
  "I'm stuck on this problem: <description>

What I've tried:
1. <attempt 1>
2. <attempt 2>

Error/behavior I'm seeing: <details>

Suggest solutions or debugging approaches."

Architecture Decisions

Get input on design trade-offs:

codex exec -m gpt-5.2 -c model_reasoning_effort="xhigh" -C . \
  "I need to decide between these approaches for <feature>:

Option A: <description>
Option B: <description>

Given this codebase, which approach is better and why? Consider maintainability, performance, and consistency with existing patterns."

Alternative Approaches

When you want a fresh perspective:

codex exec -m gpt-5.2 -c model_reasoning_effort="xhigh" -C . \
  "Here's my current approach to <problem>: <description>

What are alternative ways to solve this? What am I missing?"

Workflow Examples

Pre-Implementation Review

codex exec -m gpt-5.2 -c model_reasoning_effort="xhigh" -C . \
  "Review this implementation plan for a user authentication system:

1. Add JWT middleware to Express routes
2. Create /auth/login and /auth/register endpoints
3. Store refresh tokens in Redis
4. Add rate limiting on auth endpoints

Identify missing pieces, security concerns, or better approaches."

Pre-Commit Review

git diff --staged | codex exec -m gpt-5.2-codex -c model_reasoning_effort="xhigh" \
  "Review these changes for a PR. Check for:
- Bugs or logic errors
- Security vulnerabilities
- Performance issues
- Missing error handling
- Test coverage gaps

Provide specific line-by-line feedback."

Long-Running Migration

For complex, multi-file refactors, use gpt-5.1-codex-max:

codex exec -m gpt-5.1-codex-max -c model_reasoning_effort="xhigh" -C . \
  "Help me migrate this codebase from Express to Fastify.

Review the current structure and create a detailed migration plan.
Identify all files that need changes and potential breaking changes."

CI/Automation

For CI environments, use CODEX_API_KEY:

# In CI environment
CODEX_API_KEY=${{ secrets.CODEX_API_KEY }} \
  codex exec -m gpt-5.2-codex -c model_reasoning_effort="xhigh" \
  --json "Review this code" > review.json

GitHub Actions Example

- name: Code Review with Codex
  env:
    CODEX_API_KEY: ${{ secrets.CODEX_API_KEY }}
  run: |
    git diff origin/main...HEAD | codex exec \
      -m gpt-5.2-codex \
      -c model_reasoning_effort="xhigh" \
      -o review.txt \
      "Review this PR diff for bugs and security issues"

Best Practices

When to Use Codex Advisor

• Complex changes affecting multiple systems
• Security-sensitive code (auth, crypto, input validation)
• Performance-critical sections
• Unfamiliar codebases or languages
• When you've been stuck for >30 minutes

When NOT to Use

• Simple, obvious changes (typos, formatting)
• Trivial bug fixes with clear solutions
• When you need to move fast on low-risk changes
• Repetitive tasks where the pattern is established

Tips for Better Results

1. Provide context: Include relevant file paths, error messages, and what you've tried
2. Be specific: Ask focused questions rather than "review everything"
3. Use -C .: Let Codex see your codebase for context-aware advice
4. Choose the right model: gpt-5.2 for general, gpt-5.2-codex for code, gpt-5.1-codex-max for complex
5. Verify suggestions: Always validate Codex's recommendations against your codebase

Security Considerations

• Codex sends code to OpenAI's servers for analysis
• Review your organization's policies before sharing proprietary code
• Avoid sending sensitive credentials, API keys, or PII in code samples
• Use API keys with appropriate rate limits for usage monitoring

Troubleshooting

"stdin is not a terminal"

When piping data, always use codex exec:

# Wrong - interactive mode doesn't support piped input
git diff | codex -m gpt-5.2 "Review this..."

# Correct - use exec for non-interactive execution
git diff | codex exec -m gpt-5.2 "Review this..."

"Command not found"

# Check installation
which codex

# Reinstall if needed
npm install -g @openai/codex

Authentication errors

# Re-authenticate interactively
codex --login

# Or set API key
export OPENAI_API_KEY="your-key"
export CODEX_API_KEY="your-key"  # For CI

Rate limiting

For heavy usage, use an API key with appropriate tier limits rather than ChatGPT authentication.

No output / empty response

Ensure stderr is handled separately from stdout:

# Capture output properly
codex exec -m gpt-5.2 -c model_reasoning_effort="xhigh" \
  "Your prompt" 2>/dev/null > output.txt

# Or use -o flag
codex exec -m gpt-5.2 -c model_reasoning_effort="xhigh" \
  -o output.txt "Your prompt"