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Core Web Vitals Optimization: LCP, INP, and CLS in 2026

Core Web Vitals are the three field metrics Google uses to score real-user experience: Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS). They're a soft ranking factor on their own but a strong proxy for the engagement signals that matter more.

LCP under 2.5s

Almost always image-bound. Preload the hero image, serve it in AVIF or WebP, set explicit width/height, and host it on a CDN with HTTP/3. Defer everything that isn't above-the-fold.

INP under 200ms

INP replaced FID in March 2024. The fix is the same as for long tasks: break up JavaScript work, debounce input handlers, and move heavy logic off the main thread with Web Workers where possible.

CLS under 0.1

Reserve space for every image, embed, and ad. Avoid injecting content above existing content. Use font-display: optional or matched fallback font metrics to prevent FOIT/FOUT shift.

Measure in the field

Lab tools (Lighthouse) lie. Use Chrome UX Report (CrUX) data and a RUM tool like web-vitals.js to capture real visitor metrics segmented by device and country.

Free tools to apply this

FAQ

Do Core Web Vitals affect ranking?

Yes — Google confirmed they're a ranking signal in their Page Experience update, though the effect is small compared to relevance and authority.

What's a 'good' INP score?

Under 200ms at the 75th percentile of real visits. Between 200ms and 500ms is 'needs improvement'.

Why does my Lighthouse score differ from CrUX?

Lighthouse is a lab test on a single device. CrUX is real visitors across all devices and connections — it's the score Google actually uses.

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