Introduction
Have you ever been reading an article on your phone, tablet, or computer when suddenly the content shifts, causing you to lose your place? We’ve all been there, and it can be frustrating. This phenomenon is known as cumulative layout shift (CLS), and in this article, we’ll explore what it is, why it happens, and how to minimize it for a better user experience. So, let’s dive in and get a clearer understanding of CLS!
1. What Is Cumulative Layout Shift?
1.1 Defining CLS
Cumulative Layout Shift (CLS) is a metric that measures the unexpected shifting of elements on a webpage during its loading process. It’s a crucial aspect of web performance, as it directly affects the user experience. A high CLS score indicates that the page’s layout is unstable, causing frustration for users who might lose their reading position or accidentally click on unintended links.
1.2 How Is CLS Measured?
CLS is calculated by considering the impact fraction and distance fraction of an element. The impact fraction refers to the area that an element takes up in the viewport, while the distance fraction represents the distance an element has moved. These two factors are then multiplied to get the layout shift score for each individual element. The CLS score is the sum of all layout shift scores on a page.
2. Why Does Cumulative Layout Shift Happen?
2.1 Late-loading Images And Media
One common cause of CLS is when images, videos, or other media elements don’t have specified dimensions. As a result, the browser doesn’t know how much space to reserve for them. Once the media loads, the page’s layout shifts to accommodate the newly-loaded content.
2.2 Dynamic Content
Another culprit for CLS is the insertion of dynamic content, such as advertisements, pop-ups, or banners. When these elements load, they often push existing content out of the way, causing the layout to shift unexpectedly.
2.3 Web Fonts
Custom web fonts can also cause layout shifts. Browsers often render fallback fonts initially, then swap them with the custom font once it’s loaded. This switch can lead to layout shifts if the custom font has different dimensions than the fallback.
3. Minimizing Cumulative Layout Shift
3.1 Specify Dimensions For Images And Media
To prevent late-loading media from causing CLS, always include width and height attributes for images, videos, and other media elements. This allows the browser to reserve space for the content and reduces layout shifts.
3.2 Use CSS Aspect Ratio Boxes
Another technique for reserving space for media elements is to use CSS aspect ratio boxes. By setting the aspect ratio of a container, the browser can calculate the dimensions of the media element and reserve space accordingly.
3.3 Optimize Font Loading
To avoid layout shifts caused by web fonts, consider using the font-display property in your CSS. This property allows you to control how fonts are rendered during the loading process, helping to minimize layout shifts.
3.4 Reserve Space For Dynamic Content
When inserting dynamic content like ads or banners, reserve space for these elements in advance. This way, the content won’t push existing elements around when it loads, preventing layout shifts.
3.5 Use CSS Transitions
For elements that change position or size, using CSS transitions can help mitigate layout shifts. By smoothly animating these changes, you can minimize the impact on the user experience.
4. Tools To Measure And Optimize CLS
4.2 Chrome DevTools
Chrome DevTools is a powerful set of web developer tools built directly into the Google Chrome browser. The Performance panel in Chrome DevTools allows you to measure CLS and diagnose layout shifts by recording and analyzing page load events.
4.3 WebPageTest
WebPageTest is an online tool that provides a comprehensive performance analysis of your webpage, including CLS scores. It offers various testing locations, connection speeds, and browser configurations, allowing you to evaluate your site’s performance under different conditions.
4.4 Google Search Console
The Core Web Vitals report in Google Search Console helps you monitor the performance of your website, including CLS, for real users. This report helps you identify pages with poor CLS scores and provides guidance on how to improve them.
4.5 LanternSEO
If you’re concerned about poor Cumulative Layout Shift (CLS) on your website, LanternSEO can help. With our easy-to-use platform, you can identify and monitor CLS issues over time, and take steps to improve your website’s overall user experience.
To get started, simply sign up for an account and enter your website’s URL. Our advanced tools will analyze your site’s performance and provide you with detailed insights on any CLS issues. From there, you can monitor your progress over time and track your success as you work to improve your CLS score.
In addition to our powerful analytics tools, we also offer personalized recommendations and expert guidance to help you optimize your site for better CLS. With LanternSEO, you can rest assured that you’re doing everything possible to provide your users with the best possible experience on your website.
5. Conclusion
Cumulative Layout Shift (CLS) is a crucial aspect of web performance, as it directly impacts the user experience. By understanding the causes of CLS and implementing the strategies outlined in this article, you can create webpages that offer a stable and enjoyable experience for your users.
FAQs
1. What is Cumulative Layout Shift (CLS)?
Cumulative Layout Shift (CLS) is a metric that measures the unexpected shifting of elements on a webpage during its loading process. It affects the user experience and is an essential aspect of web performance.
2. How is CLS calculated?
CLS is calculated by multiplying the impact fraction and distance fraction of an element to get the layout shift score. The CLS score is the sum of all layout shift scores on a page.
3. What are the main causes of CLS?
The main causes of CLS include late-loading images and media, dynamic content, and web fonts. These factors cause the layout to shift unexpectedly during the page loading process.
4. How can I minimize CLS?
To minimize CLS, specify dimensions for images and media, use CSS aspect ratio boxes, optimize font loading, reserve space for dynamic content, and use CSS transitions.
5. What tools can I use to measure and optimize CLS?
You can use tools like Google Lighthouse, Chrome DevTools, WebPageTest, LanternSEO and Google Search Console to measure CLS and optimize your website’s performance.