I recently ran across someone pointing out and that their page performance scores for their website are high — all in the green zone 90s — and asking why they were still failing core web vitals.
They shared this image for the google web dev tools.
Indeed we can see the performance score is high, but the ‘Core Web Vitals Assessment’ has failed.
This is not an uncommon scenario. Let me explain why.
a. The assessment is based on the aggregate of your pages, over a period of time (28 days) — not this specific page. One page can pass while others fail. A page may load fast at the time of testing, but during period of heavy or even moderate usage may get slow down. It will also slow down if other sites on the server are getting higher traffic, or if there are hidden tasks running on the server.
b. The score of performance is NOT the same as Core Web Vitals. They are related, but not the same. The Core Web Vitals are the 6 aspects (LCP, FID, CLS, FCP, INP, TTFB), shown at the top of the page. It is possible… and not uncommon… to have a ‘fast’ site, but fail core web vitals like we see here. This is usually the result of plugging in WP Rocket or other cacheing plugin but not addressing issues in the source code. Keep in mind WP rocket is a great plugin, and I use it, but it will not fix coding issues.
On the flip side I’ve seen sites scoring low in the 40s on the performance score for nearly all pages, that still pass core web vitals.
For this site, I would start by addressing the Time To First Byte (TTFB) problem. 2 seconds is an incredibly long TTFB. Under 500ms is ideal and realistic. Further TTFB impacts the other vitals that are in the red here; FCP and LCP.
Troubleshooting Core Web Vitals
When it comes to correcting the failures of a site the place to start is in Google Search Console. Within Search Console is a Core Web Vitals Report and it tells you specifically why your sites is failing the Core Web Vitals.
Here’s an example and follow the arrows to get to it in your search console.
This site is failing specifically because of CLS issue. And it gives the 115 URLs that are failing.
CLS issues are the common reason that sites fail Core Web Vitals. It’s not hard to get the site ‘moving fast’ with hosting and a caching plugin, but CLS issues require coding changes to fix.
If you don’t have Search Console set up on your site, do it advisable to get it up and monitor it so you for any of these Core Web Vital failures. I check my sites’ Core Web Vitals’ weekly, and address issues before they result in a ‘fail’. In addition to that, it will also help your site get crawled and indexed faster — particularly for new sites.