What is Core Web Vitals?

Site Speed as a Crucial Metric for SEO

Site speed has become one of the most important metrics in SEO (Search Engine Optimization) work. This is because a “fast website” brings several benefits.

Core Web Vitals

Core Web Vitals are a set of specific technical factors that Google considers important for the end-user experience on a website. These metrics focus on page load speed to improve user experiences.

These metrics include:

  • Largest Contentful Paint (LCP)
  • First Input Delay (FID)
  • Cumulative Layout Shift (CLS)

In short, Core Web Vitals refer to three key metrics that Google uses to algorithmically scale user page experience.

Core Web Vitals take a user-centric approach, setting Google’s standards for site speed and defining which sites are considered good or bad based on these three core metrics.

Field Data and Lab Data

Google evaluates a site’s speed based on two types of data: field data and lab data. These metrics contain valuable information.

Field data is collected anonymously from Chrome users’ browsing experiences and stored in CrUX data sets. This Real User Monitoring (RUM) provides highly valuable data as it directly represents real user experiences.

Lab data, on the other hand, is obtained through tools like Lighthouse, which test the website under certain conditions in a controlled environment.

Using tools like PageSpeed Insights (PSI), you can see your website’s speed performance in both field and lab settings and observe Google’s diagnoses and recommendations for your site.

Importance of Core Web Vitals

Core Web Vitals play a crucial role in measuring user experience (UX) in terms of loading speed, making them important for both the SEO world and websites. Website owners who want to provide a good page load experience to their users should optimize their sites to meet these metrics.

Google’s long-standing advice has been to “create sites/content for users, not for Google.” Core Web Vitals exemplify this principle.

Core Web Vitals Metrics

Largest Contentful Paint (LCP)

LCP focuses on the largest content element loaded on a mobile page. It evaluates the rendering time of this element from when the page starts loading. Ideally, this element should load within 2.5 seconds. LCP is a user-centric metric related to page loading.

To optimize LCP, consider the following:

  • Optimize server response time (reduce TTFB).
  • Compress and minimize JavaScript and CSS files.
  • Optimize images (compress and use responsive images).
  • Use caching and CDN services.

First Input Delay (FID)

FID measures the time from when a user first interacts with a page (e.g., clicks a button) to when the browser responds to that interaction. This interaction should occur within 100 milliseconds.

To optimize FID, consider:

  • Compressing and combining JavaScript files.
  • Reducing the number of JavaScript files.
  • Deferring non-critical JavaScript.

Cumulative Layout Shift (CLS)

CLS measures visual stability, evaluating how much visible content shifts unexpectedly during loading. This score should be below 1, with 0.25 being acceptable.

To optimize CLS, consider:

  • Setting dimensions for images and videos.
  • Avoiding dynamically injected content that can cause layout shifts.
  • Using CSS to reserve space for elements.

Additional Recommendations

To complement Core Web Vitals, ensure your site is:

  • Mobile Friendly: Test mobile compatibility.
  • Safe Browsing: Implement security measures against phishing and malware.
  • Using HTTPS: If not already, switch to HTTPS.
  • Avoiding Intrusive Interstitials: Do not use disruptive pop-ups.


Core Web Vitals are essential for creating a healthy, user-friendly website. By focusing on LCP, FID, and CLS, website owners can significantly improve user experience and comply with Google’s standards for site speed.

Tools for Measuring Web Vitals

Use the following tools to measure and improve your Core Web Vitals performance:

  • Lighthouse
  • PageSpeed Insights
  • Chrome DevTools
  • Search Console
  • Web Vitals Chrome extension
  • Chrome UX Report API

Leave a Reply

Your email address will not be published. Required fields are marked *