Web Performance in 2026: Core Web Vitals Optimization Guide

Web Performance in 2026: Core Web Vitals Optimization Guide

Google's Core Web Vitals directly impact search rankings. INP (Interaction to Next Paint) replaced FID in 2024, and it is a much harder metric to optimize. Here is the complete playbook.

LCP: Largest Contentful Paint (< 2.5s)

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Preload the hero image: <link rel="preload" as="image" href="hero.webp">

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Use responsive images with srcset and sizes attributes

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Serve WebP/AVIF with a CDN that handles format negotiation

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Inline critical CSS, defer everything else

INP: Interaction to Next Paint (< 200ms)

INP measures the worst interaction latency during the page lifecycle. Heavy JavaScript is the enemy:

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Break long tasks with scheduler.yield()

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Use CSS transitions instead of JavaScript animations

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Virtualize long lists with react-window or TanStack Virtual

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Move heavy computation to Web Workers

CLS: Cumulative Layout Shift (< 0.1)

Set explicit dimensions on images and embeds. Use font-display: optional to prevent FOUT layout shifts. Reserve space for dynamic content with CSS aspect-ratio or min-height.