Resources/Glossary/Core Web Vitals

SEO Glossary

Core Web Vitals

Google's LCP, INP, CLS page-experience metrics.

Core Web Vitals are Google's set of page experience metrics used as a ranking signal. The three metrics are: LCP (Largest Contentful Paint) — how long it takes for the main content to load, INP (Interaction to Next Paint) — how responsive the page is to user interactions, and CLS (Cumulative Layout Shift) — how stable the layout is as the page loads.

Google's target thresholds: LCP under 2.5 seconds (good), under 4 seconds (needs improvement), over 4 seconds (poor). INP under 200ms (good). CLS under 0.1 (good). Pages passing all three are considered to have a good page experience.

Core Web Vitals are measured using real-user data from Chrome (CrUX data), not just lab-based testing tools. A page can score well in PageSpeed Insights but still fail in the field if real users experience slower loads due to network conditions or device capabilities.

Example

A page with a hero image that is not properly preloaded may have an LCP of 5+ seconds. Fixing the image delivery typically cuts LCP by 40-60% on mobile.

Apply this in practice

Definitions are step one.

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