Core Web Vitals Explained: LCP, INP & CLS

Core Web Vitals are three measurements Google uses to judge how a page feels to real people: how quickly the main content appears, how quickly the page responds when someone taps or clicks, and whether things jump around while it loads. They form part of Google’s page experience signals, and they matter for a simpler reason too: slow, jumpy pages lose visitors.

The three measurements

Largest Contentful Paint (LCP): does it load quickly?

LCP measures how long it takes for the biggest piece of content in view, usually a hero image or main headline, to appear. Google considers 2.5 seconds or less good.

Interaction to Next Paint (INP): does it respond quickly?

INP measures how long the page takes to visibly respond after someone interacts with it, such as tapping a menu or a button. It replaced the older First Input Delay metric in March 2024. 200 milliseconds or less is good.

Cumulative Layout Shift (CLS): does it stay still?

CLS measures how much the layout unexpectedly moves while the page loads, the classic case being a button that jumps just as you go to tap it. A score of 0.1 or less is good.

Google assesses each metric at the 75th percentile of real visits, so at least three out of four page loads need to hit the target for a page to pass.

How to check your site

PageSpeed Insights shows real-world data from Chrome users (where there’s enough traffic) alongside a lab test with suggestions.
Google Search Console has a Core Web Vitals report grouping your URLs into good, needs improvement and poor, based on real visits.
Lighthouse, built into Chrome’s developer tools, runs lab tests that are handy for diagnosing problems, although lab results won’t always match what real visitors experience.

The fixes that matter most

For LCP

Serve images in modern formats such as WebP or AVIF, at the size they’re actually displayed.
Don’t lazy-load the main hero image, and preload it if it’s the largest element.
Reduce render-blocking CSS and JavaScript, and use fast hosting with a CDN.
Load web fonts efficiently and keep the number of font files small.

For INP

Ship less JavaScript. Heavy themes, page builders and stacks of third-party scripts are the usual culprits.
Break up long tasks so the browser can respond between them.
Audit chat widgets, tag managers and tracking scripts, and keep only what earns its place.

For CLS

Give images, videos and embeds explicit width and height so space is reserved before they load.
Reserve space for banners, adverts and cookie notices instead of pushing content down.
Use font loading strategies that minimise text reflow when web fonts arrive.

Why we build for this from day one

Retrofitting performance onto a slow template is painful and rarely complete. It’s far easier to design and build with these limits in mind from the start: lean code, carefully chosen fonts, images handled properly and scripts kept to a minimum. That’s how every website we build is made, and it’s a core part of our technical SEO work on existing sites.

Relevance and helpful content still matter most for rankings. But when two pages are equally useful, the faster, steadier one gives both Google and your visitors a reason to prefer it.

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