What each one measures
LCP, the time until the largest block of the first screen is painted: good below 2.5 seconds. INP, how long the page takes to answer a tap or a click. And CLS, how much the content moves while loading, which is what makes you tap the wrong thing.
They are measured twice: in a lab, with a tool, and with real visits. The second one rules, because that is the one Google uses.
The thresholds: when each one is good
Google sets three thresholds: LCP is good up to 2.5 seconds, INP up to 200 milliseconds and CLS up to 0.1. They are measured at the 75th percentile of real visits, so it is not enough for the page to work well on your computer: it has to work well for three visits out of four.
INP replaced FID in March 2024. FID only measured the wait before the first response; INP measures every interaction of the visit, which is why script-heavy pages fail it more often.
How to measure Core Web Vitals
With real visit data: the Core Web Vitals report in Search Console and PageSpeed Insights, both based on the Chrome User Experience Report. With lab data: Lighthouse and the browser developer tools, which help find the cause but do not tell you what your visitors experience.
If the site has little traffic there is no real data and only the lab is left. Then you measure several times, on mobile and on a slow network, because a single measurement misleads.
What ruins them on a site built with AI
Almost always the same: images served at their original size, fonts that arrive late and shift the text, a notice that appears once you were already reading, third party scripts that block painting, and a first screen that waits for an API call before it can draw.
None of that shows at build time: it shows by measuring the published page, on mobile and on a slow network.
How we measure them and what you get
We measure every published page on mobile and desktop, with Lighthouse and with a real browser, and we repeat the measurement before opening a finding, because a single run lies. You get which element is the LCP of each page, what delays it and how much is gained by removing it.
It is part of the website review, along with security, accessibility and visibility on Google and in AI engines.