Core Web Vitals, Explained for Founders (Not Engineers)
The three metrics behind your Lighthouse performance score, in plain English.
“Core Web Vitals” shows up in every performance audit and most founders nod along without ever being told what the three letters actually measure. They're Google's published, standardized metrics for real page-load experience. LaunchGraded scores two of the three directly — LCP and CLS — as part of the Performance dimension; INP is included below because it's part of the same Google standard and worth understanding even though it isn't yet a separate LaunchGraded check.
The three metrics
| Metric | What it measures | Google's “good” threshold |
|---|---|---|
| Largest Contentful Paint (LCP) | How long the largest visible element takes to render | Under 2.5 seconds |
| Cumulative Layout Shift (CLS) | How much visible content moves after it first appears | Under 0.1 |
| Interaction to Next Paint (INP) | How responsive the page feels to a click, tap or keypress | Under 200 milliseconds |
LCP: the “is this actually loading” metric
LCP is usually your hero image, your headline block, or a large above-the-fold graphic — whichever element is the biggest thing the browser paints. A slow LCP is almost always one of a few specific causes: an unoptimized image served at full resolution instead of a web-appropriate size, a render-blocking script or stylesheet delaying everything else, or a slow server response before the page can start rendering at all.
CLS: the “did the page just jump” metric
CLS is the one visitors feel even when they can't name it — you go to tap a button and the page shifts a moment before your finger lands, because an image or ad loaded in above it. The fix is almost always the same: reserve space for anything that loads asynchronously (images, embeds, ads, cookie banners) so the layout doesn't need to rearrange once it arrives.
INP: the newest of the three
INP replaced an older metric called First Input Delay in 2024 as Google's standard responsiveness measurement. It captures how long the page takes to visibly respond after a real interaction — a click that doesn't do anything for half a second feels broken even if it eventually works. Heavy JavaScript running on the main thread at the moment someone clicks is the usual cause.
Why this matters beyond the score
Core Web Vitals are part of Google's page-experience signals for search ranking, but the more immediate cost is behavioral: a visitor who experiences a slow, jumpy, unresponsive page forms an impression of the product before they've read a word of your pitch. Our performance checklist guide goes through the specific mistakes we see most on new sites, and the free scan reports your actual LCP and CLS numbers, not just a single opaque score.