Web Performance Optimization: A Practical Checklist

Speed Is Money

Amazon found that every 100ms of latency cost them 1% in sales. Google found that 53% of mobile users abandon sites that take over 3 seconds to load. Performance isn't optional — it's a competitive advantage.

The Optimization Checklist

Images (Often the Biggest Win)

Images typically account for 50-70% of a page's total weight.

• Use modern formats: WebP for photos, SVG for icons and illustrations
• Responsive images: Serve different sizes for different viewports using srcset
• Lazy loading: Load images only when they enter the viewport
• Compression: Use tools like Sharp or Squoosh for optimal quality/size ratio
• CDN delivery: Serve images from edge locations nearest to users
• Blur placeholders: Show low-res previews while full images load

JavaScript

• Code splitting: Load only the JS needed for the current page
• Tree shaking: Remove unused code from your bundles
• Dynamic imports: Lazy load heavy components (charts, editors, maps)
• Minimize third-party scripts: Each analytics or chat widget adds weight
• Use Web Workers: Offload heavy computation from the main thread

CSS

• Remove unused styles: Use PurgeCSS or Tailwind's built-in purging
• Critical CSS: Inline above-the-fold styles in the HTML
• Avoid layout thrashing: Batch DOM reads and writes
• Use CSS containment: Tell the browser which parts of the page are independent

Caching

• Browser caching: Set appropriate Cache-Control headers for static assets
• CDN caching: Cache HTML, CSS, JS, and images at the edge
• Service Workers: Enable offline access and instant repeat visits
• Stale-while-revalidate: Serve cached content while fetching updates

Server

• Use HTTP/2 or HTTP/3: Multiplexed connections for parallel loading
• Enable compression: Brotli for text assets (20-30% smaller than gzip)
• Edge functions: Run server logic closer to users
• Database optimization: Index queries, use connection pooling

Measuring Performance

Use these tools to benchmark and monitor:

1. 1.Lighthouse — Google's audit tool built into Chrome DevTools
2. 2.WebPageTest — Detailed waterfall analysis from real locations
3. 3.Core Web Vitals report — Real user data from Google Search Console
4. 4.Vercel Analytics — Real-time performance monitoring for Next.js

Quick Wins Checklist

If you're short on time, prioritize these high-impact optimizations:

1. 1.Compress and convert images to WebP
2. 2.Enable lazy loading for below-the-fold images
3. 3.Implement code splitting (automatic in Next.js)
4. 4.Set Cache-Control headers for static assets
5. 5.Enable Brotli compression on your server/CDN
6. 6.Remove unused CSS and JavaScript
7. 7.Preload critical fonts
8. 8.Use a CDN for static assets

The Bottom Line

Web performance optimization is an ongoing practice, not a one-time task. Build performance budgets into your development workflow, measure regularly, and treat regressions as bugs. Your users — and your conversion rates — will thank you.