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Google began gradually rolling out its page experience update in June 2021, and is expected to be in full effect by August. It's important to learn the scope of these changes and how they'll impact your SEO strategy.
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Last year, Google announced that they would be updating Search to include new page experience signals in their ranking algorithm. Originally targeted for May 2021, the launch of the Google page experience update was delayed but finally began rolling out in mid-June. The rollout will be gradual—starting with more pages eligible to appear in the Top Stories carousel feature—and will be in full effect by the end of August. It’s important for marketers to know and understand the scope of these changes and especially what they mean for SEO. The new ranking criteria are designed to put an even greater emphasis on the speed and usability of websites. Faster sites with better user experiences will be rewarded with overall higher search result rankings compared to any otherwise equal counterpart website. The factors that matter most for determining the quality of performance and experience of sites are known as the Core Web Vitals.

What are Core Web Vitals?

Core Web Vitals are a set of real-world, user-centered metrics that quantify key aspects of the user experience. They measure dimensions of web usability such as load time, interactivity and the visual stability of content as it loads. They join existing signals—including mobile-friendliness, safe browsing, secure (HTTPS) connections and guidelines around intrusive interstitials—that are considered by Google when generating link placement in search results.

Core Web Vitals are comprised of three metrics:

  1. Largest Contentful Paint (LCP) measures loading performance Loading performance is determined by the render time of the largest image or text block visible within the viewport, relative to when the page first started loading. Usually this is the "hero" area. Sites should shoot for an LCP of 2.5 seconds or less across mobile and desktop.
  2. First Input Delay (FID) measures interactivity In this context, interactivity is the time from when a user first interacts with a page (i.e., clicking a link, tapping a button or using a custom JavaScript-powered control) to the time when the browser actually begins processing these event handlers in response to that interaction. An FID of 100 milliseconds or less across mobile and desktop is ideal!
  3. Cumulative Layout Shift (CLS) measures visual stability This is the sum-total of all individual layout shifts for every unexpected change in position that occurs during the entire lifespan of a page. Layout shifts are common when browsing pages on mobile connections and slow-leading elements like images or ads eventually pop into place—forcing other elements to move around without warning. Sites should aim to have a CLS score of 0.1 or less across mobile and desktop.

What sort of impact will this have?

The true impact of the Core Web Vitals signal is yet to be seen. Guidance from Google indicates mobile site rankings will be affected first and foremost, with desktop possibly to follow. It’s worth noting that drastic changes are not expected—pages with the highest-quality, most relevant information overall will still be prioritized. However, in cases where there are many pages with similarly relevant content, page experience can be much more important for visibility than Search. In addition to ranking, Google is experimenting with other incentives for producing great website experiences. There have been reports of Search results adding a visual indicator—a badge or icon—to well-performing sites that pass the Core Web Vitals assessment. There’s even been testing of “Fast Page” labels in Chrome on Android. And it’s no longer necessary for publishers to offer their content in Google AMP (Accelerated Mobile Pages) format for their links to get more prominent placement.

How does Google collect data for Core Web Vitals?

Google monitors and collects data for Core Web Vitals by maintaining a database of anonymized statistics aggregated from real Chrome browser users. (But not all users—only those who have opted-in to syncing their browsing history, have not set up a Sync passphrase and have usage statistic reporting enabled.) Known as the Chrome User Experience Report (CrUX), this data is surfaced in many Google tools:

  • PageSpeed Insights
  • BigQuery projects
  • CrUX Dashboard in Data Studio
  • Search Console

Information is collected for all viewed pages on a site (including non-indexed, non-public pages) and updated every 28 days. Because of the reliance on Chrome to gather this performance data, be aware that traffic from other browsers (Firefox, Safari, Edge) and iOS devices (where Chrome is actually using Safari’s WebKit engine) will not be represented in CrUX and therefore will not be reflected in Core Web Vitals. To classify the overall performance of a page or site, Google uses the 75th percentile value of all page views to that page or site. In other words, if at least 75% of page views to a site meet the Good threshold, the site is classified as having good performance for that metric. Conversely, if at least 25% of page views hit the Poor threshold, the site is classified as having poor performance. This means that to pass Google’s Core Web Vitals assessment, at least 75% of page loads must score:

  • Good for LCP (Load in 2.5 seconds or less)
  • Good for FID (Respond in 100 milliseconds or less)
  • Good for CLS (Layout shifts totaling 0.1 or less)

The status for an entire page is determined by the lowest, worst-performing status of the three metrics. So, if two metrics scored as Good and one metric scored as Needs Improvement, the entire page would be classified as Needs Improvement and would not pass the assessment. Fortunately, evidence of some performance improvement over time, even if not to the threshold of all three metrics passing, can still lead to some level of ranking boost. Once a page achieves a Good status, a maximum ranking boost may be applied and further optimizations will not have an effect.

Is there a way to check Core Web Vitals for a specific URL?

PageSpeed Insights

PageSpeed Insights (PSI) is the easiest and quickest way to see Core Web Vitals measurements for any URL. PSI reports results from two different sets of sources—field data and lab data—and there’s a critical distinction between the two. Field data is collected from real Chrome users who are actually loading and interacting with a page; this data is pulled from CrUX. Lab data is generated from tools used to simulate a page in a consistent, controlled environment. Lab data is useful for troubleshooting and debugging performance issues. But, because it was produced under simulated network conditions (loading on a mid-tier Android device over a worldwide-average 3G connection), the measurements are often "worst-case scenario.” This isn’t always representative of modern U.S. connection speeds and devices. The numerical performance score summary at the very top of the page is informed by lab data and other metrics but not by field data, so there's no need for marketers to panic. Chances are the tested URL is performing better for real-world users! Look to field data for whether the tested URL passes the Core Web Vitals assessment.

Google Search Console

Website owners can also sign into Google Search Console to track Core Web Vitals page performance. It’s normal for performance to vary over time since content and functionality updates can lead to different measurements. Because actual page views are the source of CrUX data, changes in traffic for the month can lead to a different distribution of scores (which is expected). An advantage to monitoring Core Web Vitals in Search Console? The new mobile and desktop reports that are offered. These reports are designed to display a site’s performance as a whole and to precisely identify issues affecting groups of pages (but not individual URLs). Fixes can also be validated over a 28-day window.

Want to score better on Core Web Vitals?

There are several general optimization strategies developers should follow to improve page performance and score better on Core Web Vitals.

Improving all Core Web Vitals

  • Minimize the amount of heavy, upfront, render-blocking CSS and JavaScript. Less is more.
    • Remove unused code. It's amazing how extra functions, plugins and style definitions can bloat the size of libraries.
    • If possible, componentize scripts and styles to load on a per page (not global) basis.
  • Defer loading of non-critical scripts and styles to later in the document or upon user interaction—especially for third-party resources.
    • Third-party resources include Google Maps, social feeds, reCAPTCHA & cookie modules, YouTube video player embeds and analytics tags.

Improving Largest Contentful Paint (LCP)

  • Preload critical images and fonts; lazy-load the remaining images.
  • Properly size and compress images.

Improving First Input Delay (FID)

  • Avoid long-running JavaScript tasks.
  • Stick to transform and opacity changes for smoother animations.

Improving Cumulative Layout Shift (CLS)

  • Specify height and width attributes for all assets.
  • Reserve space on the page for dynamically-added content.
  • Avoid inserting new content above existing content.
  • Take care when placing non-sticky elements near the top of the viewport.
  • Ensure text remains visible during WebFont load.

What should we expect for the future of Core Web Vitals?

Google will continue to evolve Core Web Vitals annually, with future enhancements and additions to come. Already, bugs in calculating CLS have been found and addressed in newer versions of Chrome. Aside from the three current metrics, Google collects additional timing data that may ultimately become part of Core Web Vitals—including First Paint, First Contentful Paint, Time to First Byte, Total Blocking Time and Time to Interactive. Other experience factors such as accessibility are also being evaluated for inclusion. Google’s benchmarks are valuable, but remember that Core Web Vitals and CrUX, by definition, do not reflect the experience of all users. Optimize for Core Web Vitals while keeping in mind that performance should be continually monitored for improvement—not only for SEO benefits, but for the positive impact on users and the corresponding increases in engagement and conversions.