With the official announcement of the Core Web Vitals, Google has caused quite a stir. The search engine giant has introduced metrics for monitoring and evaluating the usability of a site , which will also have an impact on the Google ranking: LCP, FID & CLS are the first Core Web Vitals and more metrics are to follow. What exactly stands behind these three abbreviations, how and where they can be measured and why you should get to grips with the Core Web Vitals right now, you will find out in this blog post. You'll also get some background on LCP, FID & CLS as well as some hands-on optimization tips.

The hype surrounding Core Web Vitals

With its Webmasters blog article "Evaluating page experience for a better web" from May 28, 2020, Google has caused quite a stir. There, the search engine giant announces to improve the ranking algorithm in the category usability in the course of a Google update and to introduce the so-called Core Web Vitals as (partly new) metrics to measure the user experience. 

It is no secret that websites should not only be optimized for search engines, but also for users. What good is a good positioning in the search results if your visitors leave site without having done anything? However, it is not only the content that decides whether many people find what they are looking for on your website. Usability is also decisive when it comes to whether users feel comfortable and find their way around site or whether they quickly search for alternatives according to the click-and-go principle. Users who quickly find what they are looking for in the search results are happy Google customers - so it is clear that the search engine giant also cares about the user experience. 

So why exactly is this Google article causing such considerable furore? Because Google updates are almost never announced and, when they are, they're certainly not announced with such a long lead time. The update will only be rolled out next year and there's going to be another reminder six months in advance too. 

A note on timing for the Core Web Vitals from the Google Webmasters Blog

Added to this is the somewhat lurid name of the metrics at the center of the update: Core Web Vitals. The metrics are thus not just the "vital organs" of a website but the "core" of the "vital organs" of a website. 

Google couldn't be clearer with this message. The Google Page Experience update and the associated Core Web Vitals are going to be very important for webmasters and SEOs alike. But what are these Core Web Vitals anyway?

LCP, FID and CLS - the first three of many Core Web Vitals to come

Put simply, Core Web Vitals are metrics that measure universally relevant facets of the user experience on a website, regardless of user location and context. 

The Core Web Vitals currently include three metrics:

• Largest Contentful Paint (LCP)
• First Input Delay (FID) and
• Cumulative Layout Shift (CLS).

The metrics measure different facets of the user experience of a website. While LCP focuses on loading time, FID deals with interactivity and CLS measures the visual stability of a website. 

All three metrics essentially deal with the same question: what causes website visitors not to perform any action on the website during the loading process? The Core Web Vitals provide the following answers to this question: 

1. The site doesn't load correctly and not fast enough (LCP). 
2. The site is loading but the user can't interact despite clicking or pushing (FID).
3. The site loads and the user can click but the click doesn't lead to the desired interaction (CLS).

Although LCP, FID and CLS will not really become relevant until 2021, they are already available in some analysis tools. For example, Core Web Vitals can be viewed in Google Search Console, Google PageSpeed Tools, Lighthouse and Webpagetest.org. So there is more than one way to get a Core Web Vitals report.

Google has also already announced these three metrics won't be the last. For starters, the Core Web Vitals will be combined with Google's existing search signals for website experience, namely:

• Mobile friendliness
• Safe browsing
• HTTPS and 
• Intrusive interstitial guidelines.

In addition, the Web Core Vitals will be updated and expanded annually. But that's all still a long way off. Let's first take a closer look at the ones we already have: LCP, FID, and CLS.

Largest Contentful Paint - LCP definition

The LCP measures how much time passes until the largest content block within the display area has been rendered and is therefore visible. Why exactly is the largest visible content element observed by the LCP? Google considers its load time to be the most important because it most closely reflects the perceived loading time from the user's point of view, i.e. the time from the click on the search result to the moment when the relevant bulk of a website is visible.

In most cases, the largest content element is an image, a video or a larger text portion. Which content element was specifically used to measure the LCP of an individual URL can be easily seen in PageSpeed Insights can be easily seen.

Google also provides very specific thresholds to make the LCP evaluable. The loading time of the largest content block in the viewport is considered good if it's less than 2.6 seconds. Improvements are needed for loading times between 2.6 seconds and four seconds. If the LCP is over four seconds, it's classified as poor. 

Google also cites a 75 percent limit as a further threshold: LCP, like the other Core Web Vitals, is a key figure at site level. Looking at the domain as a whole, at least 75 percent of all subpages should have a good LCP - i.e. less than 2.6 seconds. This 75 percent limit also applies to the other two Core Web Vitals FID and CLS.

First Input Delay - FID definition

The FID indicates how much time elapses from the first interaction of the user with a website until the browser reacts to this interaction. 

Interaction includes clicking on a button or link, entering text in a blank field, navigating by clicking in a drop-down menu and much more. This means clicks and keystrokes are measured. Scrolling, however, is not one of the interactions measured via by FID.

FID is relevant as a user experience metric because users often click on elements or perform similar actions during the loading process. If the website doesn't react, the visitor's user journey is interrupted. 

Google again provides three clear thresholds for the FID metric. FID should be below 100 milliseconds to be considered good. Between 100 and 300 milliseconds needs improvement. An FID is considered poor if more than 300 milliseconds elapse between the first user interaction and the browser's response time.

Cumulative Layout Shift - CLS definition

I'm sure everyone's had the following annoying experience when visiting a site before. You see straight away where you'd like to go and, exactly in the second you're about to click, a new element, e.g. a banner, loads and shifts the entire layout so you unwillingly end up clicking something else instead. The CLS is on the trail of this problem. This metric indicates how visually stable a website is in its loading process.

The basis of the CLS measurement is the multiplication of the so-called distance fraction with the impact fraction. These values answer two different questions regarding the layout displacement. The distance fraction indicates how large or far the displacement of the layout is and the impact fraction shows which part of the display area is affected by the layout shift.

The example in Figure 1 illustrates how this metric is calculated. Here, two consecutive frames are compared in a loading process. In frame A, you can see the rendered image takes up exactly half (50%) of the entire viewport, i.e. the page display area. In frame B, the image has shifted down by exactly ¼ (25%) of the display area. The distance fraction is therefore 0.25. For users, however, the layout shift has changed the view of ¾ (75%) of the entire viewport. The impact fraction is therefore 0.75. Multiplying the distance fraction and impact fraction results in a Layout Shift Score of 0.1875.

According to Google, only shifts with a CLS score of less than 0.1 are good. A score greater than 0.25 is considered poor. The score in the left example, 0.1875, is in the middle range and therefore needs improvement.

Tips for Core Web Vitals optimization

As mentioned above, the Google Page Experience update will come sometime in 2021 and we'll also get another heads-up six months in advance. This means you don't need to take any immediate action to optimize the Core Web Vitals just yet. Moreover, enough user data needs to be collected first to be able to provide the Core Web Vitals status. The fact this is still a work in progress is evident from the Core Web Vitals report in PageSpeed Insights. In many cases, you can only access laboratory data for an evaluation in this report. For field data, on the other hand, there's often not enough Chrome user data available.

There are still ways to start improving right now, however. You can use the Google Search Console report, for example, to evaluate whether and which URLs are worthy of optimization in terms of Core Web Vitals. The Google Search Console evaluates the entire website. Once you've identified affected URLs in the GSC, you can enter these URLs in PageSpeed Insights to get specific recommendations for action. A Core Web Vitals quick check of individual URLs is also available swiftly and conveniently via the Web Vitals extension for Chrome.

Core Web Vitals - is the hype justified?

Webmasters will have wide range of tools at their disposal to identify opportunities for FID, LCP, and CLS optimization. Google has made it crystal clear that these three initial Core Web Vitals are going be important. 

Nevertheless, the hype surrounding the Core Web Vitals Hype seems a bit exaggerated in parts. 

For one thing, two of the three metrics are key figures that already existed before they were titled "Core Web Vitals". FID and LCP aren't new metrics but their importance has certainly been emphasized by the new classification as Core Web Vitals. Cumulative Layout Shift (CLS) is the only truly "new" metric. And yet the same applies to CLS as to the other two metrics: websites should be optimized for users and not just for search engines. And that's nothing new!

On the other hand, Google itself stresses that content will continue to be the most decisive ranking factor:

Put simply: if a website has particularly relevant content, but only a moderate Core Web Vitals score, it will almost certainly continue to rank well. The Google Page Experience will therefore become the position-deciding criterion in strongly competing sectors where there are several websites with similarly good content.

Nevertheless, the Core Web Vitals offer a very good opportunity to present presentable evaluations of the UX based on hard metrics with clear boundaries. In this way, it can be shown very quickly and clearly whether and to what extent problems exist in the area of user experience and which measures are necessary for pagespeed optimization or usability improvement.