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Core Web Vitals Test

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Core Web Vitals Checker.

The Core Web Vitals checker measures the 3 key metrics that, according to Google, are essential to delivering a great user experience on the web. To perform the Core Web Vitals test this tool is powered by real-world Chrome user data. 

Core Web Vitals Test

What are the Core Web Vitals?

The Core Web Vitals are a set of metrics (Largest Contentful Paint, First Input Delay & Cumulative Layout Shift) designed to measure user experience. The Web Vitals are part of the Google Page experience signals together with existing Search signals for page experience, including mobile-friendliness, safe-browsing, HTTPS-security, and intrusive interstitial guidelines. Core Web Vitals are important metrics, because Google will start using them as ranking signals starting in 2021.

Google Page experience signals

Core Web Vitals test report

  • Load time – Largest Contentful Paint (LCP), measures the render time of the largest image or text block visible within the viewport.
  • Interactivity – First Input Delay (FID), the time between a user action and browser response.
  • Visual stability – Cumulative Layout Shift (CLS), the sum of individual layout shift scores, during page load.

Core Web Vitals Check

Core Web Vitals score evaluation

 GoodNeeds improvementPoor
Contentful Paint (LCP)<2500 ms<=4000 s>4000 ms
First Input Delay (FID)<100 ms<=300 ms>300 ms
Cumulative Layout Shift (CLS)<0.1<=0.25>0.25

How to pass the Core Web Vitals test?

Core Web Vitals Score

  • Pass – Your page scores meets the recommended targets at the 75th percentile for all of the above three metrics.
  • Fail – Your page scores doesn’t meet the recommended targets.

How to optimize for Core Web Vitals?

#1 Optimize Largest Contentful Paint time

When it comes to technical website optimization there is no “one-size-fits-all” solution, but when we look at the most common causes for a slow Largest Contentful Paint.

  • Slow server response times.
  • Render-blocking JavaScript and CSS.
  • Slow resource load times.
  • Client-side rendering.

#2 Optimizing First Input Delay

The main reason for a low FID score is caused by heavy JavaScript execution. Here are some examples to help with optimizing your FID.

  • Reduce heavy JavaScript execution.
  • Split code that blocks the main thread for more than 50 ms.
  • Use Web workers to make it possible to run JavaScript on a background thread.

#3 Optimize Cumulative Layout Shift

In many cases a high CLS score is related to:

  • Images that don’t have their dimensions specified.
  • Ads, embeds, and iframes without dimensions
  • Dynamically injected content

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2 thoughts on “Core Web Vitals Test

  1. Danny Longhurst

    Hi I get this message
    Sorry, Google does not have enough real-world data available for this URL.
    And a blank content body are in the page image capture.

    Any help?

    • Jasja ter Horst (admin)

      Hi Danny,

      Thank you for your comment.
      I also had a look at the URLs you refer to and because Google does not have enough real user data for them it’s unfortunately not possible to conclude if they pass the Core Web Vitals requirements.

      Hope this explains the results from the tool.


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