Google has caused quite a stir with the official announcement of Core Web Vitals. 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. In this blog post, you can find out what exactly is 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. In addition to all the background information on LCP, FID & CLS, you will also get some initial hands-on optimization tips.

The current hype surrounding Core Web Vitals

Google caused quite a stir with its Webmasters blog article "Evaluating page experience for a better web" from May 28, 2020. In it, the search engine giant announced that it would be improving the ranking algorithm in the usability category as part of a Google update and introducing the so-called Core Web Vitals as (partly new) metrics for measuring the user experience. 

It's 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 the site without having achieved anything? However, it's not just the content that determines whether people find what they're looking for on your website. Usability is also crucial when it comes to whether users feel comfortable and find their way around the site or whether they quickly leave and explore 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 is the Google article causing such a stir? Because Google updates are almost never announced and if they are, then certainly not with such a long lead time. The update is not due to be rolled out until next year and there will also be an additional reminder 6 months in advance. 

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

In addition, there is the - rather lurid - name of the metrics at the center of the update: Core Web Vitals - are not only "vital organs" of a website, but even the "core pieces" of the "vital organs" of a website. 

Google could hardly say it any clearer: the Google Page Experience Update and the associated Core Web Vitals are becoming very important for webmasters and SEOs alike. But what are Core Web Vitals anyway?

LCP, FID & CLS - Three first Core Web Vitals and more to come

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

Currently, the Core Web Vitals list three metrics, namely...

• 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 the LCP focuses on loading time, the FID deals with interactivity. The CLS, on the other hand, measures the visual stability of a website. 

Basically, however, all 3 metrics deal with the same question: What causes website visitors to stop taking any action on the website during the loading process? The Core Web Vitals provide the following answers to this question: 

1. The page does not load correctly and not fast enough (LCP). 
2. The page loads, but I can't interact with it despite clicking or pushing (FID).
3. The page loads and I can click, but the click does not lead to the desired interaction (CLS).

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

Google has also already announced that it will not stop at the three metrics. On the one hand, the Core Web Vitals will be combined with Google's existing search signals for the website experience, namely:

• Mobile Friendliness
• Safe Browsing
• HTTPS and 
• Intrusive Interstitial Guidelines

In addition, the Web Core Vitals are to be updated and expanded annually. But that is still a long way off. So for now, let's take a closer look at what 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 monitored by the LCP? Because Google considers its loading time to be the most important, as it most closely reflects the loading time perception from the user's point of view - namely the time from clicking on the search result to the moment when the relevant majority of a website is visible.

The largest content element is usually an image, a video or a larger text component. PageSpeed Insights makes it easy to see which content element was specifically used to measure the LCP of an individual URL.

Google also provides very specific boundary lines to make the LCP evaluable: The loading time of the largest content block in the viewport is good if it is under 2.6 seconds. Optimizations are required for loading times from 2.6 and under 4 seconds. If the LCP is over 4 seconds, it is classified as poor. 

Google also mentions a 75 percent limit as a further guideline: Like the other Core Web Vitals, the LCP is a page-level metric. If you look at the domain as a whole, at least 75 percent of all subpages should have a good LCP - i.e. under 2.6 seconds. This 75% 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 user's first interaction with a website until the browser responds to this interaction. 

Interactions include, for example, clicking on a button or link, entering text in a blank field, clicking to navigate a drop-down menu and much more. In other words, clicks and keystrokes are measured. However, scrolling is not one of the interactions measured via the FID.

The 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 does not respond, they are interrupted in their user journey. 

Google also provides three clear threshold values for the FID. The FID should be under 100 milliseconds for it to be considered good. There is a need for optimization between 100 and 300 milliseconds. An FID is considered poor if more than 300 milliseconds elapse between the first user interaction and the browser response time.

Cumulative Layout Shift - CLS Definition

Everyone knows this frustrating moment: you arrive at a page, see immediately where you want to click and at the moment you click, a new element appears, such as a banner, which shifts the layout and which you may even click on involuntarily. The CLS is on the trail of this problem. It 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. The values answer two different questions in relation to the layout displacement: The distance fraction indicates how large or far the displacement of the layout is. The impact fraction shows what proportion of the display area is affected by the layout shift.

The example in Figure 1 helps to understand this: Two consecutive frames are compared here in a loading process. In frame A, you can see that the rendered image occupies exactly half (50%) of the entire viewport - i.e. the page display area. In frame B, the image has moved down by exactly ¼ (25 %) of the display area. The distance fraction is therefore 0.25. For the user, however, the view has changed to ¾ (75%) of the entire viewport due to the layout shift. The impact fraction is therefore 0.75. The multiplication of distance fraction and impact fraction results in a layout shift score of 0.1875.

According to Google, only shifts with a layout shift score of less than 0.1 are good. If the value is greater than 0.25, it is considered bad. At 0.1875, the score in the example on the left is therefore in the mid-range, which is worth optimizing.

First tips for Core Web Vitals optimization

As mentioned, the Google Page Experience Update will not be released until sometime in 2021 and we will also get another heads-up six months in advance. There is therefore no acute need for action on Core Web Vitals optimization yet. We also still need to collect enough user data to be able to specify the Core Web Vitals status. The fact that this is still a work in progress can also be seen in the Core Web Vitals report in PageSpeed Insights: Here you can currently often only access lab data for an evaluation. For the field data area, on the other hand, there is often still a lack of sufficient Chrome user data.

If you still want to get to work now, you can use the Google Search Console report, for example, to evaluate whether and which URLs are worth optimizing with regard to the Core Web Vitals. This is because the entire website is evaluated in the Google Search Console. Once you have identified affected URLs in the GSC, you can receive specific recommendations for action in the second step by entering these URLs in PageSpeed Insights. You can also get a quick Core Web Vitals check of individual URLs quickly and easily using the Web Vitals extension for Chrome.

Core Web Vitals - Are they worth the hype?

This means that webmasters already have enough options via various tools to identify optimization opportunities for FID, LCP and CLS. And Google has made it abundantly clear that the optimization of the three Core Web Vitals is becoming important. 

Nevertheless, some of the new hype surrounding the Core Web Vitals hype seems a little exaggerated. 

On the one hand, two of the three metrics are indicators that already existed before they were named "Core Web Vitals": FID and LCP are not new values, but their importance was certainly emphasized once again via their reclassification as Core Web Vitals. The Cumulative Layout Shift (CLS) is the only metric that is actually new. And yet the same applies to CLS as to the other two metrics: that websites should not only be optimized for search engines, but also for users. And that is not a novelty!

On the other hand, Google itself emphasizes that content will remain the most decisive ranking factor:

So 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 then becomes a position-deciding criterion in highly competitive sectors in which 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 key figures with clear boundaries. This makes it possible to show very quickly and clearly whether and to what extent there are problems in the area of user experience and which measures are necessary to optimize pagespeed or improve usability.