What does a website performance test measure?

A comprehensive performance test measures: load time, Core Web Vitals (LCP, CLS, FID/INP), total page size, number of HTTP requests, Time to First Byte (TTFB), First Contentful Paint (FCP), and specific resource-level issues.

How is the performance score calculated?

The performance score is calculated by Google Lighthouse as a weighted combination of key metrics: LCP (25%), TBT (30%), CLS (25%), FCP (10%), SI (10%). Each metric contributes to the overall score based on its importance to user experience.

What is the difference between performance score and load time?

Load time is a single duration measurement. Performance score is a composite metric that weights multiple user experience factors according to their actual impact on how users perceive your page's speed.

Browse tools

Free · Fast · Privacy-first

Website Performance Test

A complete website performance test goes beyond load time to measure every aspect of how efficiently your page loads. FixTools runs a full performance analysis covering Core Web Vitals, resource loading, and technical metrics.

⚡ Use Tool Now How it works

Cost: Free forever
Sign-up: Not required
Processing: In your browser
Privacy: Files stay local

⚡

Lighthouse-based performance score

🔒

Core Web Vitals (LCP, CLS, FID/INP)

✨

Resource size and request analysis

Web Tool

Website Speed Test

All processing happens in your browser — your files are never uploaded to any server.

🚀Open Website Speed Test

100% Free · No account · Works on any device

How to use this tool

💡

Enter your URL for a comprehensive performance analysis covering all major metrics.

How It Works

Step-by-step guide to website performance test:

1
Enter the URL to test
Paste your page URL. Test your most important pages: homepage, key landing pages, checkout page.
2
Review the overall performance score
Check the overall score (0–100). Note which category the score falls into: Good (90+), Needs Improvement (50–89), or Poor (under 50).
3
Review Core Web Vitals
Check LCP (target under 2.5s), CLS (target under 0.1), and FID/INP (target under 200ms). These are Google's key page experience metrics.
4
Review resource and opportunity recommendations
Check the resource list for oversized images, render-blocking scripts, or uncached resources. Prioritise the highest-impact fixes first.

Real-world examples

Common situations where this approach makes a real difference:

Website redesign quality gate

A development agency runs performance tests on every page template before a new website goes live. Pages must score 85+ on mobile to pass the quality gate and proceed to client handover.

Monthly performance monitoring

An e-commerce manager runs a performance test on the homepage and top 5 product pages monthly. A sudden score drop in one month reveals a new third-party chat widget adding 800KB of JavaScript.

Developer interview technical task

A candidate for a front-end developer role is given a failing performance test report and asked to identify the issues and their solutions — using the FixTools report as the basis for the task.

When to use this guide

Use this for a comprehensive performance audit — when you want a full picture of performance beyond just load time, including Core Web Vitals and resource analysis.

Pro tips

Get better results with these expert suggestions:

Use the resource breakdown to find the biggest wins

Performance audits consistently show that image optimisation delivers the biggest load time improvement for most websites. Start with the resource size report and fix the largest assets first.

Prioritise LCP over overall score

Largest Contentful Paint (LCP) is the Core Web Vital most closely correlated with user perception of page speed. A good LCP score (under 2.5 seconds) matters more than a high overall score for user experience.

Test the pages users actually visit, not just the homepage

The homepage is often the most optimised page on a site. Test your highest-traffic landing pages and most important conversion pages — these are where performance issues cost you real business.