The speed of loading websites has become a point controlled by all … But speed is not the only UX lever taken into account by Core Web Vitals. The visual stability of the page is also part of it. And it is this last point that most directly impacts the Canada Email Address List user experience. The CLS is the indicator dedicated to the calculation of visual stability: in this article, we will discuss the concrete means that will allow you to improve it.  Before we focus on the CLS, let’s put this indicator in context. As a search engine, Google is increasingly relying on user experience to provide Internet users with qualitative results.

It is in this context that Google launched in June 2021 its update of Core Web Vitals . Its goal ? Offer webmasters and SEO professionals precise indicators that measure different elements related to user experience (or UX for User eXperience). As a reminder, these three indicators are: the FID , for First Input Delay, which calculates the time it takes for the web page to accept input from the user (such as clicks on a button); the LCP for Contentful Largest Paint, which indicates the time it takes the greatest element to be displayed on the screen; the CLS , for Cumulative Layout Shift, which calculates the movement of elements during the page load phase .

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CLS: what is it and how is it calculated?

It is on this last indicator that we are going to focus.  The CLS is therefore an indicator that calculates the movement of elements during the page loading phase. web core vitals and the CLSThe CLS as presented by Google. The numerical data is a clue: from 0.25, it is considered harmful for your UX. When a user arrives on a web page, it must load in order to be displayed on the user’s screen. During this phase, the different elements that make up the page (buttons, menus, images, etc.) each load at their own speed and are displayed as soon as they are fully loaded. Sometimes, therefore, it is possible that one item is displayed on top of another. As a result, all the elements below are pushed further down the page: they move.

This is called a Layout Shift. In order to measure the movement of elements due to this phenomenon, Google has developed the “CLS” metric. The calculation of the CLS is based on two measures: fraction impact, and the impact distance. 1 | The Impact Fraction Fractional impact measures all of the screen space an element occupies before, during, and after its cumulative movement. Concretely, if an element (an image for example) occupies half of the screen and then goes down by 25%, then it will have occupied 75% of the total screen space. In this case, the fraction impact index is 0.75. example impact fractionIn this representation, the image has been shifted by 25% downwards while it occupies 50% of the screen (called a viewport).

The place of CLS in the context of the Core Web Vitals update

In total, the image will therefore have occupied 75% of the cumulative viewport. 2 | The distance fraction The distance fraction is the second component of the CLS calculation . It measures the maximum displacement made while the page is loading in the width or height direction of the screen, whichever is greater. Thus, the CLS takes into account the size and orientation of the user’s screen. For example, on a mobile held in portrait position, it is the movements in height that will be counted by the Distance Fraction. In our previous example, the unstable element has moved 25% downwards: the distance fraction is therefore 0.25. The CLS is calculated with the Impact Fraction and the Distance Fraction, just multiply one by the other. Still using our example, this gives us: CLS = 0.75 x 0.25 = 0.1875 Google considers a good CLS to be less than 0.1.

The situation is more serious if the CLS exceeds 0.25: it is then considered bad by Google. Obviously, many tools present this clue to you automatically. First, you can turn to Google Page Speed ​​Insights which gives you the choice to analyze your page using field data or in a test environment, in its mobile or desktop version. You will also have access to detailed calculations for the three Core Web Vitals indicators. YouTube on Google Page Speed ​​InsightsTo the three indicators counted in SEO by Google, is added here the FCP. It tells you how fast the largest element on your page is loading. This is a useful metric, although very dependent on the user’s connection speed to field data. This is why this indicator is not taken into account by Google at all for your SEO.

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