Core Web Vitals : comprendre et améliorer les indicateurs clés d'expérience utilisateur

Core Web Vitals are a set of three key metrics defined by Google to measure and improve the essential aspects of user experience on websites: loading performance, interactivity, and visual stability.

The three Core Web Vitals metrics are:

• Largest Contentful Paint (LCP): Measures loading performance by tracking the time it takes for the largest visible content element to load. A good LCP is 2.5 seconds or less from when the page starts loading.

• Interaction to Next Paint (INP): Measures interactivity by assessing the responsiveness of the page to user input. A good INP is 200 milliseconds or less. (Note: INP has replaced the older metric First Input Delay (FID).)

• Cumulative Layout Shift (CLS): Measures visual stability by quantifying unexpected layout shifts during page load. A good CLS score is 0.1 or less.

How to understand and improve Core Web Vitals

• Measurement: These metrics are measured using real user data (field data) and are available in tools such as Google Search Console’s Core Web Vitals report, Lighthouse, PageSpeed Insights, and the web-vitals JavaScript library.

• Evaluation: Google recommends evaluating these metrics at the 75th percentile of page loads, separately for mobile and desktop devices. A page is considered good if it meets the thresholds for all three metrics at this percentile.

• Improvement tips:

  • Reduce page size and limit the number of resources (ideally under 500KB and 50 resources per page) to improve loading speed and interactivity.
  • Optimize images and fonts, use efficient caching, and minimize JavaScript blocking to improve LCP and INP.
  • Avoid layout shifts by reserving space for images and ads, and avoid injecting content dynamically without placeholders to improve CLS.

• Prioritization: Focus first on URLs marked as "Poor" in the Core Web Vitals report, then address "Needs Improvement" URLs. Use the report to track fixes and validate improvements over time.

Additional considerations

Core Web Vitals are critical but not the only factors influencing user experience. Other elements such as site security, content relevance, and overall usability also contribute to a quality experience.

By understanding and optimizing Core Web Vitals, website owners can enhance user satisfaction, improve search ranking potential, and increase conversion rates.