Core Web Vitals – Optimizing for Google’s UX Metrics

Note: This article was originally published on July 10, 2021. Some information may be outdated.

Core Web Vitals are a set of metrics defined by Google to evaluate the user experience of a web page. They focus on loading speed, interactivity, and visual stability.

These three metrics became especially important for front-end developers when they started to influence search ranking.

What are Core Web Vitals?

• Largest Contentful Paint (LCP): Measures loading performance. A good score is under 2.5 seconds.
• First Input Delay (FID): Measures interactivity. A good score is under 100ms.
• Cumulative Layout Shift (CLS): Measures visual stability. A good score is below 0.1.

Tips to Improve Core Web Vitals

Improving LCP

• Use lazy loading for images and videos
• Optimize critical rendering path
• Serve images in modern formats like WebP
• Reduce server response times

Improving FID

• Minimize main-thread blocking time
• Reduce JavaScript bundle size
• Use web workers for heavy computation
• Split code using dynamic import()

Improving CLS

• Always include width and height on images and videos
• Reserve space for ads and embeds
• Avoid injecting content above existing content
• Use CSS aspect-ratio to maintain size stability

How to Measure Core Web Vitals

You can test your site using:

• Lighthouse (in Chrome DevTools)
• PageSpeed Insights
• Web Vitals Chrome Extension
• Real-user monitoring tools

# Run Lighthouse in CLI
npm install -g lighthouse
lighthouse https://your-site.com

Improving these metrics not only helps SEO but also provides a better experience for users across devices and connection speeds.

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Originally published at letanure.dev