Core Web Vitals are Google’s attempt to measure how a web page feels to use. Not how it looks in a design tool, but how it behaves for a real person on a real phone: how quickly the main content appears, how fast the page responds when they tap, and whether things stay put or jump around while it loads.
The names sound technical, and the acronyms do not help, but the ideas behind them are things every one of us has felt. This guide translates the three Core Web Vitals into plain English, explains why Google cares, and outlines what actually moves them.
They sit within the broader work of keeping the technical foundations of your site in good order, and they are among the few ranking-related signals Google measures and reports openly.
What Core Web Vitals are, and where they come from
Core Web Vitals are a small set of metrics that Google publishes and updates through its web.dev project, and they feed into the broader page experience signals Google uses in ranking. There are three of them, each measuring a different part of the loading experience.
Crucially, they are based on data from real visitors, not a lab test run in perfect conditions. That is why a site can look fast on your office broadband and still fall short on the phones your customers actually use.
LCP: how fast the main content appears
Largest Contentful Paint, or LCP, measures how long it takes for the biggest piece of content on screen to load, usually the hero image or the main heading. It answers the question a visitor asks without realising: has this page actually loaded yet?
A slow LCP usually comes from a heavy hero image, a sluggish server, or scripts that block the page from rendering. Faster hosting, properly sized images and trimming render-blocking code are the usual fixes.
INP: how quickly the page responds
Interaction to Next Paint, or INP, measures how quickly the page reacts when someone interacts with it: tapping a button, opening a menu, ticking a box. If you have ever tapped something and waited an awkward moment for anything to happen, you have felt poor INP.
It usually points to heavy JavaScript keeping the browser busy. Reducing the amount of script a page runs, and breaking up the work so the browser can respond between tasks, is where the improvement comes from. INP replaced an older metric, First Input Delay, because it captures the full responsiveness of a page rather than just the first tap.
CLS: whether the layout stays still
Cumulative Layout Shift, or CLS, measures how much the page moves around unexpectedly as it loads. The classic frustration is reaching to tap a button, only for an image to load above it and shove everything down, so you tap the wrong thing.
CLS is usually caused by images and ads without reserved space, or fonts that swap in late and reflow the text. Setting explicit dimensions for images and embeds, and reserving room for anything that loads late, keeps the page steady.
Why they matter for SEO
Core Web Vitals are a genuine ranking factor, though a modest one. Google has been clear that strong content on a slightly slower page can still outrank thin content on a fast one; the vitals are a tie-breaker and a quality signal, not a magic lever. Because Google now judges the mobile version of your site first, as it explains in its guide to mobile-first indexing, your mobile scores are the ones that count.
The stronger argument is commercial. A page that loads slowly or jumps around loses visitors before they ever become enquiries, so improving these scores tends to help conversions as much as rankings. We make that case in full in why site speed matters for SEO.
How to improve your Core Web Vitals
The fixes are less exotic than the names suggest, and they overlap heavily.
- Compress and correctly size images, and load below-fold ones lazily.
- Reserve space for images, video and ads so nothing shifts as they load.
- Cut and defer unnecessary JavaScript so the browser can respond quickly.
- Use fast, well-configured hosting and caching so pages arrive sooner.
- Test on real mobile connections, not just a fast desktop.
Most of these fall under general technical housekeeping, and they are exactly the sort of thing a proper audit surfaces. If crawling and indexing are new to you, our beginner’s guide to what technical SEO is puts these metrics in their wider context.
Find out how your site scores
You do not have to guess how your site performs. Our free SEO audit measures your Core Web Vitals on real-world data, shows you which of the three is holding you back, and lays out the fixes in order of impact, with no obligation. It turns a vague worry about speed into a clear, prioritised list.
