Core Web Vitals Mistake Leads to 50% Drop in SEO Traffic – Here’s Why

by Toby

November 10, 2023

Core Web Vitals Mistake

Google wants fast-loading websites that render well on mobile devices. Of the hundreds of variables that Google uses to rank a website in its organic non-paid search results, site loading speed and usability on mobile devices are at the top of the list. And this is what's at the heart of Google's Core Web Vitals (CWV).

Why You Should Care

Google rewards sites that perform well in CWV with significant increases in impressions and clicks. This is made clear in our example below when the site lost some of its CWV tests and traffic plunged 50% immediately!

If you care about your website’s SEO success, which you should, this post is for you.

Backstory Of Our Example:

The site referenced in this example is in a highly competitive direct-to-consumer (DTC) dental healthcare niche.

We had been working on the SEO of this site for a year. The site experienced exponential growth in SEO traffic as seen below.
12 Months of Google Search Console Click Data

12 Months of Google Search Console Click Data

However, the client added new features and design elements to his pages to improve the social proof and grow the site's conversion rate.

But what happened next was NOT good.

With these new website changes, Google punished the site with a huge decline in organic traffic. Keep in mind that organic traffic was the 1st or 2nd largest channel of online sales, so the change negatively affected sales and profit.

3 Months of Google Search Console Click Data

3 Months of Google Search Console Click Data with Core Web Vitals Fail

So, Why Did Traffic Drop?

On Oct 15th, nine pages failed on Core Web Vitals (CWV) – these are the ones the client added features to (specifically some gifs that were not lazy loaded). Seventy-five percent (75) of the site’s traffic is from mobile devices so failing Mobile CWV killed mobile traffic and sales.

Core Web Vitals Mobile Fail

Core Web Vitals Mobile Fail

We then removed these new features and submitted the fix to Google via Search Console, and CWV scores came back up within days, along with the traffic. 

The specific issue causing the drop in Google traffic was a change in stability as a result of a Content Layout Shift (i.e. CLS) that increased. 

What is A Content Layout Shift (CLS)?

CLS occurs when you open a page on a website, and for a split second, the layout shifts. The problem with this is that low stability leads to a poor user experience. For example, the page loads, and you go to click on a button, the button moves, and you miss the button. This is common when you “fat finger” an action on mobile and do something you didn’t intend to.

But the good news is that once you fix the CWV issue, traffic will likely come back. And it did in our case, too. Google taketh, Google giveth.

Once the CLS issue was resolved, the mobile clicks skyrocketed back up.

Mobile Impressions Jump Core Web Vitals

Mobile Impressions Jump Core Web Vitals

What Are the Core Web Vitals (CWV)?

Google measures 3 variables in CWV for mobile and desktop (you can read more here from Google). Your score is different for each device type. But it’s designed to test your site on desktop and mobile for fast loading and good user experiences. Mobile is the hardest to score high on as Google simulates your site on an old mobile phone. The CWV variables are:

  • Loading – LCP – Largest Contentful Paint – how long it takes for the largest content piece to load for each device type
  • Interactivity – INP – Interaction to Next Paint (replaces FID, first input delay, March 2024) and is how quickly your site responds to input
  • Visual Stability - CLS - Cumulative Layout Shift – does the page shift while rendering on your screen?
    (for a deeper read on CWV, click here).

If your site has never done well on CWV, you likely haven’t experienced an increase or decrease in search traffic with any changes like this.

Toby Danylchuk

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But, if you’re in a competitive niche, like the site example above, your competitors are likely focused on CWV, so you should be too, or risk being left behind with lower SEO traffic and sales.

How To Test Core Web Vitals?

There are a number of free tools out there, and Google provides a free tool here: https://pagespeed.web.dev/. Just paste a URL, and you’ll get a score back in a few seconds. Run your competitors through it to see how they are performing. And if you’re ranking lower, low CWV scores may be partially to blame.

Also, use Google Search Console’s Page Experience and Core Web Vitals reports. Hopefully, your report looks like this:

Google Search Console - Page Experience Report

Google Search Console - Page Experience Report

And does not look like this:

Google Search Console - Page Experience Report - Failing

Google Search Console - Page Experience Report - Failing

What Do I Do If My Core Web Vitals Fail?

If you fail in your core web vitals, the first step is understanding what failed and why? Was it desktop or mobile, or both? 

From there, you need to identify what, if any, issues you can resolve. Likely, you will need a developer or SEO to help improve your scores. But if you're using a WYSIWYG (what you see is what you get) type theme, you will have some limitations on what you can do to impact faster load times.

One common issue, however, is large and slow-loading images. Ensure your images are optimized for SEO – lazy loaded, the right size for the slot on the page, and in a next-gen format (webp). These changes are usually easy and you can earn some easy wins. 

But for many issues, such as DOM script too long, you likely need to bring in the right help – an SEO, a technical web developer, or perhaps even talking to your web host, as hosting also affects performance.

The bottom line is, that the more competitive your niche, the more important CWV is to your SEO success. 

Toby Danylchuk, 39 Celsius Web Marketing Consulting

Toby Danylchuk

" Test your competitor’s pages and see how they stack up, as you could uncover a golden opportunity to take the lead from them."


Google's Core Web Vitals (CWV) are not just technical jargon. They are crucial for your website's success, particularly in SEO.

Our example illustrates how failing to meet these standards can significantly drop traffic and sales, especially on mobile devices.

But the good news is that addressing these issues can bring your traffic back once a fix is in place. As a small or medium business owner or manager, you can't afford to ignore CWV.

With a majority of web traffic now coming from mobile devices, your site's performance on these platforms is paramount.

Don't let your competitors get ahead—start by testing your website's CWV scores using tools like Google's PageSpeed Insights and Google Search Console.

If you uncover CWV issues, consider enlisting the help of SEO experts to optimize your site. This is not just about keeping up with Google's standards; it's about ensuring the best possible experience for your users, which in turn drives sales and growth.

Don't wait until it's too late—take action now to secure your website's future success.

Contact us for a comprehensive CWV analysis and personalized improvement strategies tailored to your business. Let's turn this challenge into your competitive advantage!

About the author 

Toby is the co-founder of 39 Celsius. He has over 20 years of digital marketing experience and has started several companies throughout his career. He's an expert in SEO, Social Media Ads, Google Ads, Marketing Automation, and more. He has a BA in Chemistry/Biochemistry from UC San Diego and an MBA from SDSU.

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