Optimizing your website performance with Core Web Vitals 📊

Website performance is crucial for ensuring an exceptional user experience. In a constantly evolving digital world, it's imperative to understand and optimize the Core Web Vitals, which are at the heart of the user experience for your website. This article delves deep into their meaning, operation, measurement, importance, and how to optimize them to provide a quality user experience.

Understanding Core Web Vitals

What are Core Web Vitals?

Core Web Vitals are a set of three key metrics that assess a website's performance, going well beyond simple numbers.

They immerse us in the heart of the user experience by scrutinizing three fundamental aspects:

Largest Contentful Paint (LCP): It measures more than just loading time. LCP indicates the time it takes for the main content of the page to become visible, providing valuable insight into the first impression your site leaves on the user.
First Input Delay (FID): Website responsiveness is crucial for user engagement. FID evaluates the time between the user's action (such as a click or keypress) and the site's response. A short FID means your site responds quickly to user commands, essential for a smooth experience.
Cumulative Layout Shift (CLS): A seamless user experience is not only about having a fast site. Visual stability is equally important. CLS measures the amount of unexpected layout changes on a web page. A low CLS ensures that page elements do not shift abruptly, which could disrupt visitors.

Why are they important?

These indicators are not just technical metrics; they are essential for several reasons that go beyond your website's performance:

Improved User Experience: Users are increasingly demanding, and a smooth and enjoyable experience is crucial for retaining them.
Impact on Search Engine Optimization (SEO): Search engines consider such indicators to rank websites. In the case of Google, it's certain as they champion this initiative. Better performance and experience equate to a higher ranking, meaning more visibility and organic traffic. A high rank in search results is essential for attracting a consistent flow of qualified visitors.
Reduced Bounce Rates: Visitors are more likely to stay on your site if they don't have to wait endlessly for the page to load or if the layout doesn't keep changing. A lower bounce rate indicates that visitors are satisfied with their experience on your site and are more likely to explore more pages.
Expanded Accessibility: Optimal web performance makes your site accessible to a broader audience, including those with slower internet connections or using less powerful devices. This expands your potential user base.

How to measure Core Web Vitals?

To measure the Core Web Vitals of your website, you have several free tools at your disposal, offering a detailed view of your site's performance. Here are some of these tools:

PageSpeed Insights: Provided by Google, this tool analyzes your website and provides specific recommendations to improve Core Web Vitals. It also gives you an overall performance score, allowing you to track your site's progress over time.
Lighthouse: Another Google tool that conducts a comprehensive audit of your website's performance, including Core Web Vitals. Lighthouse generates a detailed report that identifies specific issues to address to improve each metric.
Google Search Console: This platform allows you to regularly monitor your website's performance, including Core Web Vitals, and provides valuable insights to improve your ranking in search results. You can track Core Web Vitals data over time and observe how the improvements you make affect your site's performance.
Chrome UX Report: Chrome's User Experience Report (CrUX) provides measurements of user experience on how real Chrome users discover popular destinations on the web.
web-vitals: This modular library (~1.5K) is used to measure all Web Vitals metrics on real users in a way that exactly corresponds to how they are measured by Chrome and reported to other Google tools.

How to optimize Core Web Vitals?

Improving the Core Web Vitals of your website requires a strategic approach and precise adjustments for each metric. Here are some recommendations to optimize each of the three aspects:

Optimizing Largest Contentful Paint (LCP)

Image Compression: Reduce the size of images without loss of quality using image compression tools such as Squoosh, TinyPNG, or ImageOptim. This helps decrease image loading time while maintaining visual quality. You can also adopt more modern image formats like WebP, which offer better compression.
Caching: Configure caching for static resources on your server so that visitors can access frequently used elements more quickly. This reduces the overall page loading time. Use HTTP header directives such as Cache-Control to control the caching duration of resources. Regarding HTTP caching, I recommend this excellent talk by Hubert Sablonnière.
Prioritizing Critical Resources: Use the rel="preload" attribute to prioritize loading essential resources needed for the initial page rendering. Or use fetchpriority="high" on an important image displayed above the fold line. This ensures that the main content displays quickly, improving LCP. Identify critical resources using audit tools for your site and apply preloading selectively.
Use of CDN: Utilize a Content Delivery Network (CDN) to deliver your static resources from servers located near users. This reduces latency and accelerates the loading of elements, contributing to a faster LCP. CDNs are particularly effective for websites with a global audience.
Server Optimization: Ensure that your web server is optimally configured to handle HTTP requests efficiently. Use Gzip or Brotli compression to reduce the size of server responses. Configure browser caching to locally store recurring resources.

Reducing First Input Delay (FID)

Minimizing Blocking Scripts: Move non-essential scripts to the end of the HTML document or load them asynchronously. This allows the browser to continue rendering the page while downloading scripts, thereby reducing FID. Use lazy loading techniques for scripts that are not necessary for the initial page rendering.
Optimized JavaScript Code: Review and optimize your JavaScript code to eliminate inefficiencies and reduce the browser's workload. Use minification and file bundling tools to reduce the size of scripts. Split large scripts into modules for selective loading.
Use of Workers and Background Tasks: Service workers can be used to handle CPU-intensive tasks in the background, leaving the browser's main thread more responsive to user interactions. This reduces FID. You can also use web workers to run scripts in the background without affecting page responsiveness.
Resource Preloading: Use the <link rel="preload"> element to preload essential resources early in navigation. This ensures these resources are available when the user interacts with the page, reducing FID. Identify essential resources using reports from your performance analysis tools.
Removal of Unnecessary Scripts: Examine your website to identify scripts that are no longer needed. Eliminate or replace obsolete scripts with lighter solutions. Fewer scripts mean less work for the browser, reducing FID.

Minimizing Cumulative Layout Shift (CLS)

Setting Element Dimensions: Specify the dimensions of images and videos in your HTML code to reserve the necessary space upon page loading. This prevents content from shifting when it loads, reducing CLS. Use the width and height attributes to indicate media dimensions.
Space Allocation: Use <div> containers with specified dimensions to reserve space for dynamic elements. This prevents unexpected jumps in the layout when new elements appear. Avoid adding content above existing content, as it can cause unexpected shifts.
Avoiding Intrusive Ads: If your site displays ads, choose ad formats that are layout-friendly to avoid undesirable content shifts. Intrusive ads are one of the main causes of high CLS. Use responsive ad formats that adapt to available dimensions.
Asynchronous Loading of Web Fonts: If you use custom web fonts, load them asynchronously to avoid blocking page rendering. Use CSS techniques such as font-display to control the font loading behavior. Ensure that text remains readable during font loading.

Conclusion

Ultimately, Core Web Vitals are crucial for optimizing your website's performance. Understanding their impact, regularly measuring them, and implementing necessary improvements are essential to ensure your website stays performant. Remember that this is not just a technical endeavor; it's also a commitment to your users, providing them with an online experience that encourages them to stay, interact, and return.

Don't wait, start optimizing now to reach new heights in web performance. The continuous improvement of your website will keep you competitive in an ever-changing online environment and provide an exceptional user experience that will retain your visitors and strengthen your online presence.

If you have additional questions or feedback, feel free to comment on this article.

See you soon 👋

Laurent