A look back, written in 2026. Core Web Vitals arrived as part of Google's page experience update, rolled out for mobile in 2021 and desktop in early 2022. For the first time, the numbers were meant to describe what a visitor felt rather than how a test machine scored.
Three questions, not one score
Each metric answers a plain question. Largest Contentful Paint: how long before the main thing on the page is visible? Cumulative Layout Shift: does the page jump about while I am trying to read or tap it? And interactivity — first measured as First Input Delay, replaced by Interaction to Next Paint in March 2024 — asks: when I tap something, how long before the page responds?
The thresholds Google publishes for a good experience are an LCP of 2.5 seconds or less, an INP of 200 milliseconds or less and a CLS of 0.1 or less, measured at the 75th percentile of real visits. That last part is the important bit.
Field data changed the conversation
The numbers that count come from real Chrome users visiting your pages, collected in the Chrome UX Report and shown in Search Console. Not a lab test. Not your laptop on office wi-fi. Three quarters of your actual visitors have to have a good experience for the page to pass.
That ended a lot of arguments. A developer could no longer point at a fast result on their own machine, and a client could no longer be sold a fix on the strength of a screenshot. Either real visitors got a better experience over the following weeks, or they did not.
Small sites often have too little traffic for Google to report field data at all. That is not a failure — it just means you are back to testing on a real mid-range phone, which is what you should have been doing anyway.
What moved the numbers in practice
For LCP: the hero image. Sized correctly, in a modern format, not lazy-loaded when it is the first thing on the screen, and not hidden behind a slider script. On most small business sites that one image was the whole story.
For CLS: giving images and embeds their dimensions so the browser can hold the space, and not injecting banners — cookie notices, promotions — above content that is already on screen. Fonts that swap late can cause it too.
For INP: less JavaScript on the main thread. Chat widgets, heavy tag managers, several analytics tools doing the same job. Each one is small; together they make a tap feel sticky.
Where it sits in SEO
Page experience is one signal among many, and Google has said plainly that great content still wins over a faster page with worse content. I have never seen a site climb on vitals alone. I have seen plenty keep visitors they were losing.
So I treat them as a quality bar, not a growth strategy: get every template into the green, check again after anything new is added, and put the rest of the effort into pages worth reading.
