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Web Performance Glossary

Definitions and explanations of Core Web Vitals, Lighthouse metrics, and web performance terminology.

Core Web Vitals

Google's three key metrics that affect search rankings.

CLS measures visual stability. Learn what it is, thresholds, and how to prevent layout shifts.

INP measures responsiveness. Learn what it is, thresholds, and how to improve interaction speed.

LCP measures loading performance. Learn what it is, thresholds, and how to improve your score.

Additional metrics reported by Lighthouse that contribute to your performance score.

FCP measures when the first content renders. Learn what it is, thresholds, and how to improve it.

Speed Index measures visual loading progress. Learn what it is, thresholds, and how to improve it.

TTFB measures server response time. Learn what it is, thresholds, and how to optimize it.

TBT measures main thread blocking during load. Learn what it is, thresholds, and how to reduce blocking time.

TTI measured page interactivity but was deprecated in Lighthouse 10. Learn what replaced it.

Use Unlighthouse to audit all these metrics across your entire website in a single scan.

$npxunlighthouse--siteexample.com