Optimizing Codex CLI-Generated Code for Performance

Codex often generates nested loops where vectorized operations or database queries would be more appropriate, especially in Python data processing tasks. It creates new database connections per request instead of using connection pooling. Generated Node.js code may use synchronous file I/O where async alternatives exist

Replace nested Python loops with numpy/pandas vectorized operations or SQL aggregations. Implement a connection pool with pg-pool or SQLAlchemy's pool. Switch blocking file operations to their async equivalents. Add caching for expensive computations that are called repeatedly with the same inputs

Before optimizing, measure. Use your browser's Lighthouse audit to get a baseline score. Check Core Web Vitals (LCP, FID, CLS) — these directly affect your Google ranking. Use the Performance tab in DevTools to identify which components take the longest to render. For server-side performance, add timing logs to API routes to find slow endpoints.

The fastest way to improve performance: optimize and lazy-load images, enable compression on your server, remove unused CSS and JavaScript, implement code splitting so users only download code for the page they're viewing, and add proper caching headers for static assets. These changes alone can cut load times significantly.

If your Codex CLI app uses a database, slow queries are often the biggest performance bottleneck. Add indexes on columns you filter or sort by. Use SELECT to fetch only the columns you need instead of SELECT *. Implement pagination for lists — loading 10,000 rows at once will always be slow. Consider adding a caching layer for data that doesn't change frequently.