Google's Core Web Vitals testing tools take 28 days to collect aggregated field data. This is unlikely to change anytime soon.

Google search attorney John Mueller explained this during Search Central's SEO hangout recorded on March 5.

Search Engine Journal's IT director, Vahan Petrosyan, asked Müller about this and noted the challenges that the 28-day window brings with it for developers and SEOs.

When a change is made to a website to improve Core Web Vitals, it takes at least 28 days for that change to be reflected in Google's testing tools.

The 28 day window is unlikely to ever get any smaller, according to Mueller's answer, which you can read below.

John Mueller from Google on the most important Web Vitals data

Mueller doubts that the way Core Web Vitals data is collected will ever change the way it is now.

"I don't know. I doubt it because the data we're showing in the search console is based on the Chrome User Experience reporting data aggregated over those 28 days. So that's the main reason for the delay there. It is not that the search console is slow to process this data or anything like that. It's just the way the data is collected and aggregated. It just takes time. "


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It is not Google's intention to analyze and report Core Web Vitals data in real time. The results represent aggregated data because Google wants to ensure that the website provides a good user experience over a longer period of time.

If SEOs and developers want the data faster, Mueller recommends running their own tests using third-party tools or the PageSpeed ​​Insights API.

"Usually when people ask about things that say," I want to know early if something breaks, "I recommend making sure you run your own tests on your side, parallel to your importance pages, so to speak. And there are a number of third-party tools that do this for you automatically.

You can also use the Page Speed ​​Insights API directly and, I don't know, pick a small sample of your important pages and just test them out every day. This is a great way to see if there are any regressions in any of the setups you made relatively quickly. "


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Mueller points out that the laboratory data offered by third-party tools does not match the field data reported by Google.

“Obviously a laboratory test is not the same as the field data. So there is a slight difference. However, if you find that the data lab test results are stable over a period of time and then suddenly become very weird, it is a strong indicator that something has gone wrong somewhere in your layout or pages. "

Mueller recognizes that the way Google collects data makes things harder for people, and measuring cumulative layout shift (CLS) is especially difficult.

If SEOs feel that Google's calculations don't make sense, Mueller recommends that they contact the Chrome team directly.

“It makes things more difficult. It's not that we're trying to make things harder, it's just the way that this data is collected in Chrome. The aggregation only takes some time.

The cumulative layout shift is sometimes I think difficult to interpret and what exactly is causing the problems there.

I think for things that you think the calculations are being done in a way that makes little sense I would also reach out to the Chrome team. I think Annie Sullivan in particular is working on improving the cumulative layout-shift side of things. And just make sure they see these kinds of examples.

And if you come across something that you say, "Oh, that doesn't make any sense at all," make sure they know about it. It's not so much that from the Google search page we would be trying to figure out what exactly happens to that score, but we have to rely on the score from the Chrome page. "

Finally, Müller reminds SEOs that Google plans to update the Core Web Vitals about once a year.

While the cumulative layout shift is a key element of Web Web this year, it may not be next year when Google finds that it is not absolutely necessary for a good user experience.

“Our goal with the Core Web Vitals and Page Experience in general is to keep them updated over time. I think we announced that we might want to update them once a year and let people know what happens in advance.

So I would expect that to improve over time. But it's also important that you get your feedback and make sure they are aware of these strange cases. "

Hear the full discussion of Core Web Vitals in the video below:


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