Page Speed Test: How to Check & Improve Your Website Performance

Understanding Core Web Vitals

Core Web Vitals are three specific metrics that Google uses to evaluate page experience. They measure loading, interactivity, and visual stability — the three things users care about most.

Lab Data vs. Field Data

When you run a page speed test, you get two types of data:

• Lab data (Lighthouse): Simulated test on a mid-tier mobile device with throttled 4G connection. Consistent and reproducible, but doesn't reflect real user experience. Useful for debugging.
• Field data (CrUX): Real measurements from actual Chrome users over the past 28 days. This is what Google uses for ranking decisions. Requires sufficient traffic to generate data.

If your lab score is good but field data is poor, your users have slower devices or connections than the lab simulation. If lab is poor but field is good, your users tend to have fast connections. Our page speed checker shows both lab and field data side by side.

How to Fix Common Speed Issues

1. Optimize Images (Biggest Impact)

Images are usually the heaviest resources on a page. WebP delivers roughly 25–34% smaller files than JPEG at equivalent quality (Google, WebP Compression Study, 2024); AVIF can reduce file size a further 20% over WebP. Compress images, set explicit width and height attributes to prevent layout shifts, and lazy-load images below the fold. Read our full image optimization guide.

2. Minimize JavaScript

JavaScript is the most expensive resource — it must be downloaded, parsed, compiled, and executed. Remove unused code, defer non-critical scripts, and use code splitting to load only what's needed for the current page. Tree-shaking and dead-code elimination tools help identify bloat.

3. Enable Text Compression

Gzip typically reduces HTML, CSS, and JavaScript transfer sizes by 60–80%; Brotli (RFC 7932, Google, 2015) achieves 15–25% better compression ratios than gzip on text assets, according to Cloudflare's 2023 benchmarks. Most web servers and CDNs support both — Brotli is preferred for modern browsers, with gzip as the fallback.

4. Reduce Server Response Time

Time to First Byte (TTFB) should be under 800ms. Common fixes: use a CDN, implement server-side caching, optimize database queries, and consider upgrading your hosting tier. Edge computing (Vercel Edge Functions, Cloudflare Workers) can reduce TTFB dramatically.

5. Eliminate Render-Blocking Resources

CSS and JavaScript that block initial rendering delay how quickly users see content. Inline critical CSS (the styles needed for above-the-fold content), defer non-critical CSS, and add async or defer attributes to script tags.

6. Use a CDN

A Content Delivery Network serves your content from servers geographically closer to users. This reduces latency, especially for international traffic. Free CDN options include Cloudflare and Vercel's edge network. For more tips, see our site speed optimization guide.

Page Speed and AI Search

Speed isn't just about traditional SEO anymore. AI systems that generate answers need to quickly fetch and process your content. Googlebot and other AI crawlers allocate crawl budgets per domain; Google's John Mueller confirmed in 2024 that slow TTFB directly reduces how many pages Googlebot fetches per crawl session. A slow site means:

• AI crawlers may timeout or deprioritize pages that exceed 2–3 second server response times
• Competing faster sites get crawled more often and more completely, resulting in fresher index entries
• Ahrefs' 2024 crawl study (450M URLs) found that pages in the top Google ranking positions had a median TTFB of 370ms — 2× faster than pages ranking outside the top 10

Optimizing for speed supports both SEO and GEO simultaneously. Check your full SEO + AI Readiness score with a free Website Audit.

Performance Budget Recommendations

Frequently Asked Questions

Fundamentals: Learn about GEO (Generative Engine Optimization) and AEO (Answer Engine Optimization) — the two frameworks for optimizing your content for AI search engines.