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

A one-second delay in page load time reduces conversions by 7%. Google uses page speed as a ranking factor. And AI search systems increasingly prefer fast, well-structured sites. Here's how to test your page speed, interpret the results, and fix what's slowing you down.

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. Use modern formats like WebP or AVIF (30-50% smaller than JPEG). 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 and Brotli compression can reduce HTML, CSS, and JavaScript file sizes by 70-90%. Most web servers and CDNs support this — you just need to enable it. Brotli is 15-20% more efficient than gzip for text content.

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. A slow site means:

• AI crawlers may timeout before fully indexing your content
• Competing faster sites get crawled more often and more completely
• AI systems may prefer cached summaries over your actual content if your site is slow to respond

Optimizing for speed supports both SEO and GEO simultaneously. Check your full SEO + GEO score with a free Foglift scan.

Performance Budget Recommendations

Frequently Asked Questions