The Complete Web App Performance Checklist for 2024

Use this checklist to systematically improve your web app's performance. I use this exact process for client projects.

Core Web Vitals

Largest Contentful Paint (LCP) — Target: < 2.5s - [ ] Preload hero images and critical fonts - [ ] Use next/image or srcset for responsive images - [ ] Serve images in WebP/AVIF format - [ ] Implement server-side rendering for above-the-fold content - [ ] Use a CDN for static assets

Cumulative Layout Shift (CLS) — Target: < 0.1 - [ ] Set explicit width/height on images and videos - [ ] Reserve space for dynamic content (ads, embeds) - [ ] Use font-display: swap with size-adjusted fallbacks - [ ] Avoid inserting content above existing content

Interaction to Next Paint (INP) — Target: < 200ms - [ ] Break up long tasks (> 50ms) with yield patterns - [ ] Debounce/throttle user input handlers - [ ] Use CSS containment for complex layouts - [ ] Virtualize long lists

JavaScript Optimization

• [ ] Code split at route level
• [ ] Lazy load below-the-fold components
• [ ] Tree-shake unused dependencies
• [ ] Analyze bundle with webpack-bundle-analyzer
• [ ] Remove unused polyfills

Network Optimization

• [ ] Enable gzip/brotli compression
• [ ] Set proper cache headers (immutable for hashed assets)
• [ ] Preconnect to critical third-party origins
• [ ] Use HTTP/2 or HTTP/3
• [ ] Minimize third-party scripts

The Impact

Following this checklist typically yields: - 30-50% improvement in load times - 20-40% reduction in bounce rates - Measurable improvement in search rankings

Need help implementing these optimizations? Let's talk about your specific performance challenges.