What Is Core Web Vitals?
Definition
A set of Google metrics (LCP, INP, CLS) that measure real-world user experience for loading performance, interactivity, and visual stability.
Why It Matters
Core Web Vitals are official Google ranking signals. A page that fails these thresholds may rank lower than a less optimised competitor that simply loads faster and behaves more predictably — particularly on mobile devices.
How It Works
The three metrics are: LCP (Largest Contentful Paint — main content load time, target under 2.5s), INP (Interaction to Next Paint — responsiveness to user input, target under 200ms), and CLS (Cumulative Layout Shift — visual stability, target under 0.1). Data comes from real Chrome users via the Chrome User Experience Report (CrUX), not synthetic lab tests.
A news website discovers its CLS score is 0.45 because ads load after the page and push content down unexpectedly. After reserving fixed space for ads before they load, CLS drops to 0.05 — clearing the "Good" threshold and improving mobile rankings.
Quick Facts
- Core Web Vitals data comes from real users, not lab tests — lab scores can differ significantly
- Google Search Console provides free page-level Core Web Vitals reports
- INP replaced FID (First Input Delay) as a Core Web Vital in March 2024
- Image optimisation and reducing render-blocking JavaScript are the top two fixes for LCP
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