Website Performance Optimization: A Developer Guide

Performance Is a Feature

A 1-second delay in page load reduces conversions by 7%. Performance is not optional—it directly impacts revenue.

Measurement First

Before optimizing, measure:

Lighthouse performance score

Core Web Vitals (LCP, INP, CLS)

Time to First Byte (TTFB)

Total page weight

Number of requests

Quick Wins

Image Optimization

Convert to WebP/AVIF format

Implement responsive images with srcset

Lazy load below-fold images

Set explicit width/height attributes

CSS Optimization

Remove unused CSS (PurgeCSS)

Minimize critical CSS inline

Defer non-critical stylesheets

JavaScript Optimization

Code split by route

Defer non-critical scripts

Tree-shake unused modules

Use dynamic imports for heavy components

Caching Strategy

Browser Caching

Set long cache headers for static assets (1 year). Use content hashing in filenames for cache busting.

CDN

Serve static assets from a CDN. Configure edge caching for HTML pages where appropriate.

Server Caching

Implement server-side caching for database queries and API responses. Use Redis or Memcached for frequently accessed data.

Compression

Enable Brotli compression (preferred over Gzip). 15-25% smaller than Gzip for text-based assets.

Monitoring

Set up Real User Monitoring (RUM) to track performance in production. Lab data (Lighthouse) and field data (CrUX) tell different stories—monitor both.