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. Codex runs locally and provides an independent perspective using OpenAI's reasoning models.

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
export OPENAI_API_KEY="your-key"

# Option 2: First run will prompt for ChatGPT login
codex

Default Configuration

All commands use GPT-5.2 with maximum reasoning effort (xhigh) for thorough analysis:

# Base command pattern
codex -m gpt-5.2 -c model_reasoning_effort="xhigh" "your prompt"

Command Reference

Plan Review

Get feedback on an implementation plan before starting:

codex -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 -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 specific file
codex -m gpt-5.2 -c model_reasoning_effort="xhigh" -C . "Review this file for bugs, security vulnerabilities, performance issues, and suggest improvements. Focus on: <specific concerns>"

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

# Review staged changes
git diff --staged | codex exec -m gpt-5.2 -c model_reasoning_effort="xhigh" "Review these changes before commit. Check for bugs, security issues, and adherence to best practices"

Hard Problem Solving

When stuck on a difficult problem:

codex -m gpt-5.2 -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 -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 -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

Before implementing a complex feature:

# 1. Write your plan
# 2. Get Codex review
codex -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

Before committing complex changes:

# Review staged changes
git diff --staged | codex exec -m gpt-5.2 -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."

Debugging Session

When stuck on a bug:

codex -m gpt-5.2 -c model_reasoning_effort="xhigh" -C . "I have a race condition in my async queue processor.

Symptoms:
- Jobs occasionally process twice
- Happens under high load
- Logs show overlapping job IDs

Relevant files: src/queue/processor.ts, src/queue/worker.ts

Help me identify the cause and fix."

Model Selection

This skill defaults to GPT-5.2 with xhigh reasoning for maximum quality. Adjust for different needs:

# Default: GPT-5.2 with xhigh reasoning (best quality, slower)
codex -m gpt-5.2 -c model_reasoning_effort="xhigh" "Complex review..."

# Faster responses with lower reasoning (for simpler tasks)
codex -m gpt-5.2 -c model_reasoning_effort="medium" "Quick question..."

# Use o3 for alternative perspective
codex -m o3 -c model_reasoning_effort="high" "Architecture question..."

Reasoning Effort Levels

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. Iterate: Ask follow-up questions to dig deeper
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

"Command not found"

# Check installation
which codex

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

Authentication errors

# Re-authenticate
codex --login

# Or set API key
export OPENAI_API_KEY="your-key"

Rate limiting

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

"stdin is not a terminal"

When piping data to codex, use the exec subcommand for non-interactive mode:

# 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..."