Core Web Vitals are Google's three standardized metrics for measuring real-world user experience, incorporated into Google's Search ranking since 2021.
LCP — Largest Contentful Paint
- Measures: how long it takes to render the largest visible image or text block in the viewport.
- What users feel: "How fast does the main content appear?"
- Good: ≤ 2.5s | Needs improvement: ≤ 4s | Poor: > 4s
INP — Interaction to Next Paint (replaced FID in 2024)
- Measures: the latency of the worst interaction (click, keypress, tap) across the entire page visit.
- What users feel: "Does the page respond quickly when I interact?"
- Good: ≤ 200ms | Needs improvement: ≤ 500ms | Poor: > 500ms
CLS — Cumulative Layout Shift
- Measures: unexpected visual shifts of page elements during the entire lifetime of the page.
- What users feel: "Do things jump around as I try to click?"
- Good: ≤ 0.1 | Needs improvement: ≤ 0.25 | Poor: > 0.25