Digital, Web Development, Websites & Web Apps

Core Web Vitals: How to Optimise Your Site for Better Performance

Posted on by arbdigital
Core Web Vitals - Bicknell Digital | Develop. Engage. Publish.
31
Jan

Core Web Vitals are a set of performance metrics defined by Google that measure user experience on a website. These metrics—Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS)—are crucial for page ranking, usability, and engagement. Optimising Core Web Vitals is essential for faster load times, improved interactivity, and a seamless browsing experience.

This article will cover the technical aspects and how to optimise each metric for better website performance.

Understanding Core Web Vitals

Core Web Vitals focus on three key areas:

1. Largest Contentful Paint (LCP)

What it measures: The time taken to render the largest visible content (e.g., image, video, or text block) on a page.

  • Good Score: Below 2.5 seconds
  • Needs Improvement: 2.5 – 4.0 seconds
  • Poor Score: Above 4.0 seconds

2. First Input Delay (FID) [Replaced by INP in 2024]

What it measures: The time between a user’s first interaction (click, tap, or key press) and the browser’s response.

  • Good Score: Below 100ms
  • Needs Improvement: 100 – 300ms
  • Poor Score: Above 300ms

Note: Google has replaced FID with Interaction to Next Paint (INP) as a new responsiveness metric. INP tracks the longest user interaction delay instead of just the first one.

3. Cumulative Layout Shift (CLS)

What it measures: The visual stability of a webpage by analysing unexpected layout shifts.

  • Good Score: Below 0.1
  • Needs Improvement: 0.1 – 0.25
  • Poor Score: Above 0.25

How to Optimise Core Web Vitals

Optimising LCP (Largest Contentful Paint)

🔹 Optimise Server Response Times

  • Use fast hosting services (e.g., Cloudflare, AWS, Vercel).
  • Implement server-side caching (e.g., Redis, Varnish).
  • Reduce time-to-first-byte (TTFB) with optimised back-end logic.

🔹 Optimise Render-Blocking Resources

  • Defer or asynchronously load JavaScript (JS) and CSS.
  • Use critical CSS inlining to reduce blocking stylesheets.
  • Minify and compress files (e.g., using Gzip or Brotli).

🔹 Improve Image Loading Performance

  • Use Next-Gen image formats (e.g., WebP, AVIF).
  • Enable lazy loading (loading="lazy").
  • Use a Content Delivery Network (CDN) to serve images faster.

🔹 Implement Efficient Caching

  • Set long cache expiration headers (Cache-Control: max-age).
  • Use service workers to cache key assets.

Optimising INP (Interaction to Next Paint)

🔹 Reduce JavaScript Execution Time

  • Use code splitting (e.g., dynamic imports in Webpack).
  • Remove unused JS via tree shaking.
  • Use Web Workers to offload tasks from the main thread.

🔹 Optimise Event Listeners

  • Use passive event listeners ({passive: true}) for scroll and touch events.
  • Avoid expensive DOM manipulations inside event handlers.

🔹 Minimise Third-Party Scripts

  • Reduce external tracking scripts (e.g., Google Analytics, Tag Manager).
  • Load third-party scripts asynchronously (async or defer).

Optimising CLS (Cumulative Layout Shift)

🔹 Specify Image & Video Dimensions

  • Always define width and height attributes (<img width="800" height="600">).
  • Use CSS aspect ratios (aspect-ratio: 16/9;).

🔹 Avoid Late-Loading Ads & Elements

  • Reserve space for ads, banners, and embeds via CSS (min-height).
  • Use lazy loading placeholders with skeleton UI components.

🔹 Optimise Web Fonts

  • Use font-display: swap; to prevent layout shifts.
  • Host fonts locally instead of external CDNs when possible.

Testing and Monitoring Core Web Vitals

To continuously track and optimise Core Web Vitals, use the following tools:

✅ Google PageSpeed Insights – Provides detailed Core Web Vitals metrics.
✅ Lighthouse (Chrome DevTools) – Generates performance reports with actionable fixes.
✅ WebPageTest – Offers real-world testing for load speed and UX.
✅ Google Search Console – Monitors Core Web Vitals across indexed pages.

Conclusion

Optimising Core Web Vitals is a critical step for improving site performance, user experience, and SEO rankings. By focusing on LCP, INP, and CLS, developers can ensure faster load times, better responsiveness, and a visually stable web experience.

By following these technical optimisations, your website will not only meet Google’s standards but also provide a seamless, high-performance experience for users. 🚀

arbdigital

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