Cumulative Layout Shift (CLS)

Have you ever been frustrated when you clicked on a link or a button, but the page didn’t move to the expected position? Or ever tried looking for a product on an eCommerce website, only to find it has moved to another location? That’s Cumulative Layout Shift (CLS), and it’s a real problem that affects user experience and website performance. But don’t worry, because we have the solution - this guide will show you how to eliminate CLS once and for all!

Table of Contents Cumulative Layout Shift (CLS)

What is Cumulative Layout Shift (CLS)?

Cumulative Layout Shift (CLS) is a metric used to measure the visual stability of a page. It is defined by the World Wide Web Consortium (W3C) as “the sum total of all individual layout shift scores for each unexpected layout shift that occurs during the entire lifespan of the page”. In other words, it’s a measure of how often a page’s layout shifts unexpectedly.

Put simply, CLS is a measure of how often elements on a page move after the page has loaded, causing a disruption in the user experience. It can be caused by a variety of factors, such as slow loading images, content being added or removed from the page after it has loaded, or ad units that resize when they load.

It’s important to note that CLS is only an issue when it causes a disruption in the user experience. If a page’s layout shifts in an expected way, such as when the user scrolls or interacts with a page element, the CLS score will not be affected.

Why is CLS Important?

CLS is important because it impacts the user experience. When a page’s layout shifts unexpectedly, users may become frustrated or confused, and may even abandon the page altogether. This can have a negative impact on conversion rates, page engagement, and other key metrics.

For this reason, CLS has become an important ranking factor for search engines, such as Google. A page’s CLS score is taken into account when determining its search engine ranking, so it’s important to optimize your page’s CLS score in order to improve its search engine ranking.

CLS is also important for mobile users. Mobile users tend to be more sensitive to page layout shifts, and a poor CLS score can lead to a poor mobile user experience. Therefore, it’s important to optimize your page’s CLS score in order to ensure a good mobile user experience.

How to Calculate and Measure CLS

CLS is calculated using a formula developed by the W3C, which takes into account the size of the element that moved, the distance it moved, and the amount of time it took for the page to load. The formula is as follows:

CLS = (Size of the Element) x (Distance Moved) / (Time Taken to Load).

The higher the CLS score, the poorer the user experience. To measure CLS, you can use a variety of tools, such as Google PageSpeed Insights, WebPageTest, and Chrome DevTools.

Steps to Eliminate CLS

Now that you know what CLS is and why it’s important, let’s look at how to eliminate it once and for all. Here are four steps you can take to optimize your page’s CLS score:

Minimizing Render-Blocking Resources

The first step to eliminating CLS is to minimize the amount of render-blocking resources on your page. Render-blocking resources are resources that must be loaded before the page can be rendered, such as JavaScript and CSS files.

Minimizing render-blocking resources can help reduce CLS by ensuring that the page can be rendered as quickly as possible. To minimize render-blocking resources, you can use a tool like Google PageSpeed Insights to identify the resources that are causing the page to load slowly, and then optimize them.

You should also look at the structure of your page and make sure that the resources are being loaded in the correct order. For example, you should ensure that the CSS files are being loaded before the JavaScript files.

Avoiding Ads, Widgets and Embedded Content

Another way to reduce CLS is to avoid ads, widgets, and embedded content. Ads, widgets, and embedded content can cause layout shifts when they are loaded, as they can resize or move elements on the page.

To avoid this, you should try to minimize the number of ads, widgets, and embedded content on your page, or use asynchronous loading for them. Asynchronous loading means that the content is loaded after the page has been rendered, so it doesn’t cause any layout shifts.

Optimizing Images

Images can also cause layout shifts when they are loaded, as they can resize or move elements on the page. To avoid this, you should optimize your images to ensure they load quickly.

You can optimize your images by using an image optimization tool, such as ImageOptim or TinyPNG. These tools can reduce the file size of your images without sacrificing quality, which can help reduce CLS by ensuring that the images load quickly.

Using Asynchronous Loading for Third-Party Scripts

Third-party scripts, such as analytics and tracking scripts, can also cause layout shifts when they are loaded. To avoid this, you should use asynchronous loading for these scripts. Asynchronous loading means that the script is loaded after the page has been rendered, so it doesn’t cause any layout shifts.

Best Practices for CLS Optimization

In addition to the steps outlined above, there are a few best practices you can follow to optimize your page’s CLS score:

Minimize the amount of DOM elements on the page. The more DOM elements on the page, the more likely it is that elements will move when the page is rendered. Use CSS to position elements. Using CSS to position elements instead of HTML can help reduce layout shifts, as CSS is more predictable than HTML. Test your page in different browsers and devices. Different browsers and devices can cause different layout shifts, so it’s important to test your page in as many browsers and devices as possible. Monitor your page’s CLS score. It’s important to keep an eye on your page’s CLS score to ensure it remains optimized.

Tools and Resources for CLS Optimization

There are a variety of tools and resources available to help you optimize your page’s CLS score. Here are a few of the most popular ones:

Google PageSpeed Insights: This tool can help you identify the resources that are causing your page to load slowly, and then optimize them. Chrome DevTools: This tool can help you identify the elements on the page that are causing layout shifts, and then optimize them. WebPageTest: This tool can help you measure your page’s CLS score and then optimize it. ImageOptim: This tool can help you optimize your images to reduce their file size and improve performance.

Cumulative Layout Shift (CLS) Consultation

Cumulative Layout Shift (CLS) is an important metric that can have a significant impact on your page’s performance and user experience. Fortunately, there are a few steps you can take to optimize your page’s CLS score, such as minimizing render-blocking resources, avoiding ads, widgets and embedded content, optimizing images, and using asynchronous loading for third-party scripts.

By following the steps outlined in this guide, you can eliminate CLS once and for all and ensure that your page’s layout remains stable. If you need help with optimizing your page’s CLS score, contact us today for a free proposal.