Glossary
What is Core Web Vitals?
Core Web Vitals are Google's three measured page-experience metrics — loading performance, interactivity responsiveness, and visual stability — used as a factor in ranking and as a benchmark for real user experience.
The three current metrics are Largest Contentful Paint (LCP — how long the largest visible element takes to render, a proxy for perceived load speed), Interaction to Next Paint (INP — how quickly the page responds to a user's click, tap, or keypress, replacing the older First Input Delay metric in 2024), and Cumulative Layout Shift (CLS — how much visible content unexpectedly jumps around as a page loads, like a button shifting down just as someone taps it).
Google measures these primarily through real-world, anonymized user data collected via Chrome (the Chrome User Experience Report), not just a lab test run once in a controlled environment — which is why a page can score well in a lab tool like Lighthouse but still fail its real-world Core Web Vitals if actual visitors are on slower connections or older devices than the lab test simulated.
They matter for two separate reasons that often get conflated: they're a confirmed, if modest, ranking factor, and — usually the bigger effect in practice — a slow or janky page directly loses conversions regardless of where it ranks, since visitors abandon slow pages before they even get to see the offer.