Performance Rules

# Performance Rules

## Measurement First
- Profile before optimizing — never guess where bottlenecks are
- Set performance budgets (load time, bundle size, response time)
- Monitor production performance, not just dev benchmarks
- Use lighthouse, WebPageTest, or custom metrics

## Database
- Index columns used in WHERE, JOIN, and ORDER BY
- Use pagination for list endpoints — never return unbounded results
- Avoid N+1 queries — use eager loading/joins
- Cache expensive queries with appropriate TTLs

## Frontend
- Lazy-load below-the-fold content and routes
- Optimize images (WebP, proper sizing, lazy loading)
- Minimize JavaScript bundle size — analyze with bundlesize tools
- Use CDN for static assets

## Backend
- Use connection pooling for databases
- Cache at the right level (HTTP, application, database)
- Use async I/O for concurrent operations
- Return only needed fields — avoid over-fetching

## General
- Prefer algorithms with better time complexity first
- Use streaming for large data sets
- Batch operations where possible (bulk inserts, batch APIs)
- Set timeouts on all external calls