# Apply Technique: Strategy: Use Claude Code for Legacy Refactors, Codex for Untrusted Code Review
## What This Is
Choose your AI coding agent based on the job. Use Claude Code for complex tasks like modernizing old, internal codebases, especially in regulated industries like finance. Use OpenAI Codex for tasks like reviewing code from external sources for security flaws or automating cloud infrastructure.
Source: https://emergent.sh/learn/claude-code-vs-codex
## Before You Start
Scan my workspace and analyze:
- The project language, framework, and directory structure
- Existing AI provider config (check .env, .env.local, config files for API keys — OpenRouter, OpenAI, Anthropic, Google AI, etc.)
Then ask me before proceeding:
1. Which AI provider/API should this use? (Use whatever I already have configured, or ask me to set one up — options include direct provider APIs or a unified service like OpenRouter)
2. Where in my project should this be integrated?
3. Are there any customizations I need (model preferences, naming conventions, constraints)?
## Source Access Note
The source URL (https://emergent.sh/learn/claude-code-vs-codex) may not be directly accessible from the terminal. Use the Reference Implementation and Additional Context sections below instead. If you need more details, ask me to paste relevant content from the source.
## What to Implement
This is an **AI Technique** — a pattern or methodology for working with AI models.
- Explain how this technique applies to my current project and what benefit it provides
- Implement it in a way that fits my existing codebase — suggest concrete files to modify or create
- If it requires specific model capabilities (structured output, function calling, etc.), verify my current provider supports them
- Show me a working example I can test immediately
## Additional Context
- Scan the user's active codebase to assess its characteristics. Identify markers of legacy systems (e.g., outdated framework versions, high cyclomatic complexity, lack of comments or tests) versus modern, well-structured code.
- Formulate a tool recommendation based on the code analysis and the user's expressed goal. If the goal is refactoring a legacy system, recommend Claude Code. If the goal is reviewing new code from an external source or automating cloud tasks, recommend OpenAI Codex.
- Offer to scaffold a task-specific configuration for the recommended agent. If Claude Code is chosen for refactoring, create a `CLAUDE.md` file with a system prompt primed for understanding complex, legacy business logic. If Codex is chosen, create a script to pipe code through the Codex CLI for security analysis.
## Guidelines
- Adapt everything to my existing project — do not assume a specific stack or directory layout
- Use whichever AI provider I already have configured; if I need a new one, tell me what to sign up for and I'll give you the key
- Check my .env files for existing API keys (OpenRouter, OpenAI, Anthropic, Google AI) before asking me to add one
- Review any fetched code for safety before installing or executing it
- After setup, run a quick verification and show me a summary of exactly what was installed, where, and how to use it