Website Speed Optimization: A Practical Guide

Speed is a business metric

Amazon found every 100ms of latency cost 1% in sales. Google uses Core Web Vitals as a ranking signal. Users abandon pages that take more than 3 seconds on mobile. Speed optimization is not a developer side project — it directly affects revenue and search visibility.

This guide covers the highest-impact optimizations ordered by effort versus reward.

Measure before you optimize

Run Google PageSpeed Insights, WebPageTest, and a website audit to establish baselines. Focus on Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS). Fix the metric that fails thresholds first.

Image optimization (highest impact)

Images are the largest contributor to page weight on most sites. Compress every image with the image compressor. Convert to WebP with the image converter. Serve responsive sizes with srcset. Lazy-load below-the-fold images.

See our best free image compressor guide for settings by use case.

Caching and CDN

Set long cache headers for static assets (CSS, JS, images, fonts). Use a CDN to serve assets from edge locations near visitors. Configure cache busting via filename hashing so updates deploy cleanly.

Code minification and delivery

Minify CSS with the CSS minifier

Minify SVG assets with the SVG minifier

Defer non-critical JavaScript

Remove unused CSS and JS (tree-shaking in build tools)

Preload critical fonts and hero images

Server and hosting

Choose hosting with HTTP/2 or HTTP/3 support. Enable gzip or Brotli compression at the server level. Reduce Time to First Byte (TTFB) by optimizing database queries and using server-side caching for dynamic pages.

Third-party script audit

Analytics, chat widgets, ad trackers, and social embeds add latency. Audit each third-party script: does it justify its performance cost? Load non-critical scripts asynchronously. Self-host fonts instead of loading from Google Fonts when possible.

Speed optimization checklist

Hero image under 200 KB (WebP, compressed)

LCP under 2.5 seconds on mobile

INP under 200 milliseconds

CLS under 0.1

Total page weight under 1.5 MB

No render-blocking resources above the fold

Related Zovaty tools

Image compressor — reduce image weight

CSS minifier — shrink stylesheets

Website audit — performance scan

SVG minifier — optimize vector assets

Conclusion

Start with images — they deliver the biggest gains for the least effort. Then caching, then code. Measure after each change. Speed optimization is iterative, not one-time.

Core Web Vitals explained

LCP (Largest Contentful Paint) measures when the main content loads — target under 2.5 seconds. INP (Interaction to Next Paint) measures responsiveness to user input — target under 200 milliseconds. CLS (Cumulative Layout Shift) measures visual stability — target under 0.1. Failing any metric can hurt search rankings.

Google Search Console reports Core Web Vitals for your site based on real user data (field data), not just lab tests. Field data reflects actual visitor experience including slow devices and networks.

Font loading optimization

Web fonts block text rendering if loaded synchronously. Use font-display: swap to show fallback text immediately. Preload critical font files. Limit to two font families and four weight variants maximum. Self-host fonts to eliminate third-party DNS lookups.

Continuous performance monitoring

Set up performance budgets: max page weight, max LCP, max number of requests. Fail CI builds that exceed budgets. Review monthly trends in Search Console and analytics. Performance regressions often come from adding analytics scripts, chat widgets, or unoptimized images — not from code changes.

Lazy loading and resource hints

Lazy load images and iframes below the fold using loading="lazy" attribute. Preload critical resources with link rel="preload". Prefetch likely next-page resources with link rel="prefetch". DNS prefetch for third-party domains you connect to.

Speed on serverless and edge platforms

Serverless functions add cold start latency. Edge rendering reduces TTFB by serving from locations near users. Static generation eliminates server processing entirely for marketing pages. Choose architecture based on content update frequency and interactivity requirements.

Mobile-first optimization priorities

Test on real mobile devices with throttled networks, not just desktop Chrome DevTools. Mobile CPU is slower, networks are variable, and screen sizes vary widely.

Prioritize mobile LCP element — usually the hero image. Compress aggressively, preload, and serve from CDN edge.

Critical CSS extraction

Extract CSS needed for above-the-fold rendering and inline it in the HTML head. Load remaining CSS asynchronously. Tools like Critical and Penthouse automate extraction. This eliminates render-blocking CSS for initial paint.

Resource hints for faster loading

Preconnect to third-party origins you depend on: analytics, fonts, CDN. DNS-prefetch for less critical origins. Prefetch next-page resources on hover or scroll proximity for multi-page flows.

Performance audit schedule

Weekly: automated Lighthouse CI on deploy. Monthly: manual review of top 10 pages by traffic. Quarterly: full site audit including third-party script review. After every major feature launch: targeted audit of changed pages.

Use the website audit for quick monthly checks between comprehensive audits.

Summary: speed optimization priorities

Compress images first. Enable caching. Minify CSS/JS. Audit third-party scripts. Monitor Core Web Vitals monthly. Use website audit for quick checks.