Core Web Vitals: what they mean and how to fix them

Core Web Vitals are a set of metrics that Google uses to measure real world user experience on your website. They affect your search rankings directly, and they also affect whether visitors stay on your site or bounce to a competitor.

The three metrics

Largest Contentful Paint (LCP) measures how quickly the main content of your page becomes visible. Your target is under 2.5 seconds. The biggest factors are server response time, render blocking resources, and image optimization.

Interaction to Next Paint (INP) measures how responsive your page is to user interactions. Every click, tap, and keyboard input should produce a visual response within 200 milliseconds. Heavy JavaScript bundles and long running tasks are the usual culprits when INP scores are poor.

Cumulative Layout Shift (CLS) measures visual stability. When elements on your page move around unexpectedly while loading, it creates a frustrating experience. Images without dimensions, dynamically injected content, and web fonts that cause text to reflow are common causes.

Quick wins

Start with images. Use modern formats like WebP or AVIF, set explicit width and height attributes, and lazy load images below the fold. This alone can dramatically improve both LCP and CLS.

Next, audit your JavaScript. Every kilobyte of JS that ships to the browser adds to parse time and blocks interactivity. Consider frameworks like Astro that ship zero JS by default, or use code splitting to load only what each page needs.

Finally, invest in good hosting. A fast server response time is the foundation that everything else builds on. CDNs, edge caching, and modern hosting platforms can cut your Time to First Byte by 50% or more.