Core Web Vitals is a set of speed metrics that Google uses for ranking pages as part of its page experience signals, with a focus on mobile performance. The metrics, including Largest Contentful Paint (LCP), Cumulative Layout Shift (CLS), and First Input Delay (FID), will officially impact SEO rankings starting June 2021. It is essential for website owners to monitor their Core Web Vitals through Google Search Console to ensure their pages are categorized as 'good' for optimal ranking.

1. Core Web Vitals: Page Speed Is Now More Important for SEO
Core Web Vitals are the speed metrics that are part of Google’s Page Experience signals used
to measure user experience. The metrics measure visual load with Largest Contentful Paint
(LCP), visual stability with Cumulative Layout Shift (CLS), and interactivity with First Input Delay
(FID). Page experience and the included Core Web Vital metrics will officially be used for
ranking pages in June 2021.
The easiest way to see the metrics for your site is with the Core Web Vitals report in Google
Search Console. With the report, you can easily see if your pages are categorized as “poor
URLs,” “URLs need improvement,” or “good URLs.”

2. Inside the report, you can find more detailed information on the particular
issues and a list of affected pages.

4. Quick facts about Core Web
Vitals
Fact 1: The metrics are split between desktop and mobile, but only mobile
signals will be used for ranking pages. Google is switching to 100%
mobile-first indexing in March, so it makes sense to use the mobile speed
signals since the indexed pages will also be based on the mobile versions.
Fact 2: The data comes from the Chrome User Experience Report (CrUX),
which records data from opted-in Chrome users. The metrics will be assessed
at the 75th percentile of users, so if 70% of your users are in the “good”
category and 5% are in the “need improvement” category, then your page is
still judged as “need improvement.”
Fact 3: The metrics will be assessed for each page, but if there isn’t enough
data, John Mueller states that signals from sections of a site or the overall site
may be used.
Fact 4: With the addition of these new metrics, AMP is being removed as a
requirement from the Top Stories feature on mobile. Since new stories won’t
actually have data on the speed metrics, it’s likely that the metrics from a
larger category of pages or even the entire domain may be used for this.
Fact 5: Single Page Applications don’t measure a couple of the metrics, FID
and LCP, through page transitions. We’ll talk about what those are in a minute.
Fact 6: The metrics may change over time, and the thresholds might as well.
Google has already changed the metrics used for measuring speed in their
tools over the years as well as their thresholds for what is considered fast or
not. It’s entirely likely this will all change again in the future. In fact, we did
some work on improving the previous metrics last year, but we need to do
some work again to improve the new metrics.