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Core Web Vitals - Complete Guide for Beginners

Learn all about Core Web Vitals - what they are, why they matter, and how to improve your website's performance, accessibility, and SEO.

Core Web Vitals

What are Core Web Vitals?

Core Web Vitals are a set of essential metrics introduced by Google to measure user experience on a website. These metrics focus on three key aspects: performance, responsiveness, and visual stability. In other words, they help determine whether a website is fast, interactive, and visually stable for users.

Google has identified three main metrics within Core Web Vitals:

  • Largest Contentful Paint (LCP): Measures the time it takes for the largest visible content on the screen to load.
  • First Input Delay (FID): Evaluates a website’s responsiveness by measuring the time it takes to respond to the user’s first interaction.
  • Interaction to Next Paint (INP): Evaluates a website’s responsiveness by measuring how long the page takes to visibly react to the user’s interactions, not just the first one.
  • Cumulative Layout Shift (CLS): Measures visual stability by calculating how much page elements move during loading.
An example page loading in the browser. 1. The page starts loading. 2. The main content takes a while to show up. 3. You click and nothing happens. 4. Everything moves while it loads. 5. Each feeling has a name: LCP, INP and CLS.

These metrics are essential to understanding how users perceive the quality of a website and how they impact SEO.

Why are Core Web Vitals Important?

Core Web Vitals are not only important for developers but also for website owners and marketers. Here’s why:

  1. Impact on SEO: Google uses these metrics as ranking factors in its search algorithm. Good performance in Core Web Vitals can improve your search engine ranking.
  2. User Experience: A fast and stable website improves user satisfaction, reduces bounce rates, and increases conversions.
  3. Accessibility: A website that loads quickly and is interactive is more accessible to users with slow connections or older devices.

In summary, optimizing Core Web Vitals not only benefits users but also contributes to the overall success of your website and improves your SEO.

How to Measure Core Web Vitals

Measuring Core Web Vitals is easier than it seems. Google offers several free tools to help you evaluate your website’s performance:

  1. Google PageSpeed Insights: Provides a detailed analysis of your website’s performance, including Core Web Vitals metrics.
  2. Google Search Console: Includes a specific Core Web Vitals report showing how your website is performing in terms of LCP, FID INP, and CLS.
  3. Lighthouse: An auditing tool integrated into Chrome DevTools that allows you to perform real-time tests.

These tools will give you a clear view of the areas that need improvement to optimize your SEO.

Good Practices to Improve LCP

Largest Contentful Paint (LCP) is one of the most important metrics as it measures the loading speed of the main content. Here are some good practices to improve it:

  1. Optimize images and videos: Use modern formats like WebP and compress media files to reduce their size.
  2. Use lazy loading: Delay the loading of images and videos that are not initially visible on the screen.
  3. Minimize resource blocking: Reduce the execution time of JavaScript and CSS that block rendering.
A filmstrip of a page load, one frame every half second, with the LCP moment marked. 1. Unoptimized: the main image lands at 3.5 s. 2. Lighter images: it lands at 2.5 s. 3. Lazy loading what is off screen: 2 s. 4. Less render-blocking JavaScript and CSS: 1 s.

By following these practices, you can ensure that your website loads quickly and provides a good user experience, which also benefits your SEO.

How to Reduce FID INP

First Input Delay (FID) Interaction to Next Paint (INP) measures your website’s responsiveness. A low FID INP is crucial to ensure users can interact with your site without delays. Here are some tips:

  1. Reduce JavaScript code: Remove unnecessary scripts and optimize essential ones.
  2. Use Web Workers: Offload heavy tasks to background threads to avoid blocking the main thread.
  3. Prioritize resource loading: Load critical resources first to make the site interactive as soon as possible.
  4. Break up long tasks: Split heavy work into shorter tasks and yield the main thread between them (for example with scheduler.yield() or setTimeout), so the browser can handle a click in between.
A timeline of the browser's main thread, with a click that arrives while it is busy. 1. You click during a long task and have to wait for it to finish. 2. Less JavaScript: a shorter task, a shorter wait. 3. Part of the work moves to a Web Worker and frees the main thread. 4. Critical work first: the click is handled and the heavy work comes after.

These actions will help your website respond quickly to user interactions, improving both user experience and your SEO.

Improve Visual Stability with CLS

Cumulative Layout Shift (CLS) measures how much page elements move during loading. A high CLS can be frustrating for users. Here’s how to improve it:

  1. Define dimensions for images and videos: Specify the width and height of media elements to avoid layout shifts.
  2. Avoid inserting dynamic content above existing content: If necessary, reserve space to avoid unexpected movements.
  3. Use preloaded web fonts: This prevents text from resizing during loading.
An example page with the expected position of each block dashed and its actual position on top. 1. Everything lands below where it should be. 2. With width and height, the browser reserves the image space. 3. No content inserted on top: the space is reserved first. 4. Preloaded fonts: the text does not jump and the layout settles.

With these practices, your website will be visually stable and more pleasant for users, which also contributes to better SEO.

Conclusion

Optimizing Core Web Vitals is essential to improving performance, accessibility, and the overall user experience on your website. By following the good practices mentioned, you will not only improve your search engine ranking (SEO) but also create a more efficient and enjoyable website for your visitors.

Start measuring and optimizing today!

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