Core Web Vitals is Google's attempt to measure whether a page feels good to use, and it feeds into search rankings. There are three of them, and each one maps to a moment of frustration you've had on someone else's site.
1. Largest Contentful Paint — "when does the page actually appear?"
LCP measures how long it takes for the biggest thing on screen — usually a hero image or a headline block — to finish loading. It's the moment the page stops looking blank and starts looking like a page.
Good: under 2.5 seconds. Needs work: 2.5–4. Poor: over 4.
Usual culprits: a huge unoptimised hero image, a slow server, or fonts and scripts that block rendering. The fix is almost always "make the big image smaller and load it sooner."
2. Interaction to Next Paint — "when I tap something, does it respond?"
INP measures the delay between you interacting with the page — tapping a button, opening a menu — and the page visibly reacting. If you've ever tapped a menu three times because nothing happened, that's bad INP.
Good: under 200 milliseconds. Needs work: 200–500. Poor: over 500.
The cause is nearly always too much JavaScript running on the main thread, often from third‑party widgets. Fewer scripts, or scripts that load later, fixes it.
3. Cumulative Layout Shift — "why did the button move as I went to tap it?"
CLS measures how much the page jumps around while it loads. An ad or image loads in above what you were reading, everything shifts down, and you tap the wrong thing. That's layout shift.
Good: under 0.1. Needs work: 0.1–0.25. Poor: over 0.25.
The fix: reserve space for images, ads, and embeds before they load, so nothing has to push its way in.
How to check yours
Run your site through PageSpeed Insights. The scores at the top marked "Core Web Vitals Assessment" are what matter — that's real data from real Chrome users on your site, not a lab simulation. Anything failing is worth fixing.
Why it's worth doing
The ranking effect is real but modest — Google uses Vitals as a tiebreaker, not a primary signal. The bigger win is conversion. Faster, steadier pages keep more people around and turn more of them into enquiries. The SEO benefit is a bonus on top of a site that simply works better.
If your report is a wall of red and you'd rather not wade through it, performance work is one of the things we do.