Testing, tools and monitoring
How to measure speed the right way with PageSpeed Insights, Lighthouse, Search Console and DevTools, and how to catch slowdowns early.
A speed number is only useful if you know what produced it. A lab test, a real-user report and a browser tool answer different questions, and mixing them up is the most common reason people chase the wrong fix.
Start with the idea. How to measure Core Web Vitals explains the two kinds of data. Then pick the tool you need: PageSpeed Insights for a first look, Lighthouse for the lab test itself, the DevTools Performance panel and Network panel for the cause, and WebPageTest and other tools for the rest.
To see real visitors, read about the Chrome UX Report and real user monitoring. To catch a slowdown early, use automated tests and budgets. To make changes safely, read how to test speed changes safely and testing on real phones.
Guides in this topic 10 guides
- How to measure Core Web Vitals: tools compared
Which tool answers which question: PageSpeed Insights, Search Console, Lighthouse, Chrome DevTools and the web-vitals library, and when to trust each number.
- PageSpeed Insights explained: how to read your report
A walkthrough of the PageSpeed Insights report: the real-user result, the lab score, the insights and diagnostics, and what each tells you to do.
- Lighthouse: what it tests and how to run it
Lighthouse is Google's free audit tool. What it checks, four ways to run it, the settings that change your score, and what a lab test can and cannot tell you.
- DevTools Performance panel: how to record and read it
The Performance panel shows what the browser did as a page loaded or responded. How to record, read the tracks and long tasks, and find what slows it.
- DevTools Network panel: how to read a page load
The Network panel lists every file a page requests. How to set up a fair test, read the waterfall and the timing phases, and find the files that slow a page.
- WebPageTest and other speed tools: what each is for
PageSpeed Insights, Lighthouse, DevTools, WebPageTest and field data answer different questions. What each measures, where it runs, and which to use when.
- Real user monitoring: measure your own visitors
Real user monitoring records the speed your visitors really get. What it adds to lab tests and CrUX, how the web-vitals library works, and how to use the data.
- Automated speed tests and performance budgets
Catch a slowdown the day it is made. What a performance budget is, how Lighthouse CI works, why one run misleads, and a routine for teams without a build.
- Testing on real phones: why it matters and how
A laptop pretending to be a phone is only an approximation. Why real devices differ, which phones to test, and how to inspect a page on a real Android phone.
- How to test speed changes safely
A speed fix can break a form, a checkout or the layout. How to test on a copy, change one thing at a time, measure fairly, check real visitors, and roll back.
Start here
Free website audit
Live Google data for any public page: mobile and desktop.
Mobile + desktop · Lighthouse lab test · Real-user Chrome data when Google has it
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