Core Web Vitals Glossary
Definitions of every performance metric Google uses to evaluate page experience — with scoring thresholds, common causes, and how to fix each one.
Largest Contentful Paint
Measures when the largest visible element finishes rendering. A Core Web Vital and direct ranking signal.
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Interaction to Next Paint
Measures worst-case interaction latency across the full session. Replaced FID as a Core Web Vital in 2024.
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Cumulative Layout Shift
Measures visual instability — how much content unexpectedly moves during and after load. Core Web Vital.
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Time to First Byte
Measures server response time. Sets the floor for every downstream metric including LCP.
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First Contentful Paint
Measures when the first piece of visible content renders. Key indicator of perceived loading speed.
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Total Blocking Time
Sums main-thread blocking between FCP and TTI. Lighthouse's proxy for interactivity (correlates with INP).
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Which metrics are Core Web Vitals?
Google's Core Web Vitals are the three metrics used as ranking signals in the Page Experience update: LCP (loading), INP (interactivity), and CLS (visual stability). The other metrics on this page — TTFB, FCP, TBT — are diagnostic tools that help you understand and fix poor Core Web Vitals scores, but are not themselves ranking factors.
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