Failed Core Web Vitals Assessment

Summary: You probably landed on this page after Pagespeed Insights told you that you have failed the Core Web Vitals assessment. And now you might be wondering why this is. In this article, we will discuss the possibilities and how you'll soon be able to pass on your Core Web Vitals.

  • by Jordy Scholing & Karlijn Löwik
  • Published
  • Reading time ± 7 minutes
  • Core Web Vitals
Failed Core Web Vitals Assessment

You're not the only one who fails the Core Web Vitals assessment. Out of all the URLs included in the Chrome User Experience Report, only 45.1% pass all 3 Core Web Vitals on desktop, and on mobile, it is only 38.5%. But to ensure that your visitors have a good technical experience on your website, you'd rather be among the domains that do succeed.

What are Core Web Vitals?

Core Web Vitals are a set of user-centric metrics that measure the loading speed, interactivity, and visual stability of a webpage. These factors directly impact the user experience (UX) and are crucial for a website's SEO ranking. The three primary Core Web Vitals are:

Google is actively sending issues for INP in search console.

Why Do Core Web Vitals Assessments Fail?

Core Web Vitals assessments can fail for several reasons, including slow server response times, large page sizes, unoptimized images, excessive JavaScript, and poor coding practices. Failing these assessments can lead to lower SEO rankings and a subpar user experience.

How does Google measure Core Web Vitals?

For starters, it's good to know where Google bases on whether you fail or pass the Core Web Vitals assessment. There is much confusion about this. Some people think that a high Lighthouse score contributes to your Core Web Vitals assessment, but this isn't true.

A 100 score on Google Lighthouse

The Lighthouse score given by google is based on a website visit under simulated conditions (lab data). This is not a representation of how your real users experience the website.

This is why Google uses field (RUM) data to decide whether you fail or pass the Core Web Vitals assessment.

Did I pass the Core Web Vitals?

Through data available through the Chrome User Experience Report, google determines whether you pass your Core Web Vitals. This data is based on visits from users who visit your website. So each one is under different circumstances and different user experiences. You can also add your product page, category page or listing page to find out what urls are failing for the Core Web Vitals.

To find out if your Web site passes the Core Web Vitals, you can use Pagespeed Insights. This is a tool that is free to use.

  1. Go to Pagespeed Insights
  2. Enter the URL you want to audit
  3. Look at the results at the top of the page (Discover what your real users are experiencing)

Core Web Vitals Assessment Failed

You now get an overview that includes the 3 Core Web Vitals and 3 additional metrics that also have to do with user experience. You can also select whether to include data from the exact URL only or the origin (including other pages of the website that have CrUX data).

The CrUX report only has data from visitors from Google Chrome, but you might have a lot of traffic entering from Safari

How to pass the Core Web Vitals assessment?

Passing Core Web Vitals is 50% about having the right mindset and knowledge at your disposal.

When you want to get started with optimizing your page speed, there are 3 phases you need to go through before you can start making actual adjustments in your code.


Before you want to start improving Core Web Vitals, you need to know how your real users (RUM) are experiencing your website. To get an overview of this you can use a tool like Pagespeed Insights, but our free UX score tool looks a little bit better.

  • It is important to know that the data you see within Pagespeed Insights has a delay of 28 days. So if you make an improvement today, you can see in 28 days whether this has had a positive or negative impact on your site speed.
  • When you make a lot of deployments you want to set up alerts for when things seem to change. Real User Monitoring (RUM) tools like RUMvision are able to do this.


After you've gained insights into performance data through monitoring, you can start doing analysis. For which Core Web Vitals are you succeeding, and on which templates (product page, category page, blog page, contact page) aren't you succeeding? You might also wonder under what circumstances and conditions your users enter your website. Getting to know your audience is one of the biggest steps in the right direction.

  • Under what Internet speeds?
  • How fast are their mobile phones?
  • Did they enter through a query string (Google / Facebook ads)?
  • Dot they have their reduced data usage turned on?


When you want to get started with Core Web Vitals or site speed in general, it can be helpful to use a page speed consultant. When you don't have the knowledge or time to pay attention to this, a consultant is an ideal solution.

Consultants often have years of experience in the field and will know what common problems within your stack are (WordPress, Magento 2, Shopify, etc.)

Consultants can also transfer knowledge to your developers over time, so they can eventually get to work monitoring and analyzing page speed data themselves.

How to Fix Core Web Vitals Assessment Failures

  • Optimize Images: Compress and resize images, use modern image formats (like WebP), and implement lazy loading to improve LCP.
  • Reduce JavaScript Execution Time: Minimize and defer non-critical JavaScript, and use the async or defer attributes to load scripts.
  • Improve Server Response Time: Upgrade your hosting plan, use a content delivery network (CDN), and implement server-side caching to enhance server performance.
  • Minify CSS and JavaScript Files: Minify and compress CSS and JavaScript files to decrease page size and improve loading speed.
  • Eliminate Render-Blocking Resources: Remove unnecessary CSS and JavaScript files, and prioritize loading critical resources to enhance page performance.
  • Avoid Cumulative Layout Shift: Reserve space for images and ads, and avoid inserting content above existing elements to prevent layout shifts.

Reasons for failing Core Web Vitals

Optimizing Core Web Vitals comes with lot of nuances. What works for you and what doesn't? Some best practices apply to you either way and so you can work on them to optimize your Core Web Vitals.

If you´ve failed your Core Web Vitals assessment on WordPress the following article is full of optimizations tips. The tips in this article will also apply if you´ve failed the Core Web Vitals assessment on Shopify.

9 Optimization tips to pass Core Web Vitals assessment

Optimizing resource loading with Priority Hints (Improve LCP)

Set the Largest Contentful Paint (LCP) image's priority higher by putting fetchpriority=high on the image element. This will make LCP happen more quickly.

With our tooling and custom dimensions, we were able to confirm the impact of adding a fetchpriority high. Even though this domain was already really fast on the LCP (1648ms) this single line of code was able to make it almost 300ms faster.

Set Width And Heights On Images And IFrames (Improve CLS)

Making sure that the width and height attributes of your images are set properly is one of the simplest things you can do to cut down on the amount of Cumulative Layout Shift (CLS). If they are not present, an image will cause the content that comes after it to shift to make room for it as it downloads.

Reduce JavaScript and plugin usage (improve FID)

The First Input Delay (FID) is a metric that is impacted a lot by JavaScript, and thus plugins. Imagine a button loading in, then it becomes visible and eventually, the user wants to click on it. By having a lot of JavaScript on your website you'll have the risk that this will keep downloading, parsing, and rendering as the site becomes visible to the user and the user not being able to click on the button.

The new Interaction to Next Paint (INP) metric will also benefit from this.


If you want to succeed on your Core Web Vitals assessment you'll have to start investing time in it. Sometimes there are quick ways to improve your page speed, but after this, you'll need to have insights into your real users. This can be achieved by setting up a real user monitoring tool.

You might even wonder if Google's thresholds are enough, as you might be interested in setting higher site speed challenges.

If you want to stick to free tools we suggest that you use our Core Web Vitals checker or Pagespeed Insights real user data, as this is what matters for UX, bounce, conversion, SEO, SERP, and ranking.

Not sure what is the perfect fit for you? Reach out to us and one of our site speed experts will be happy to talk to you.

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