Cumulative Layout Shift (CLS)
Introduction to Cumulative Layout Shift (CLS)
Cumulative Layout Shift (CLS) is a web performance metric that measures the stability of a webpage’s layout during page loading. It refers to the unexpected shifting of elements on a page that can cause a poor user experience. When users visit a webpage, they expect a smooth and stable experience. However, when the elements on a page move unexpectedly, users can get confused, frustrated, and annoyed, leading to a negative experience.
Importance of CLS
The importance of CLS lies in its impact on user experience. A high CLS score means that the layout of a page is unstable, causing elements to shift during loading, which can distract and confuse users. This, in turn, leads to higher bounce rates and a decrease in user engagement. As a result, Google has made CLS a part of its Core Web Vitals, a set of user-focused metrics that measure the overall web experience.
Causes of CLS
There are several causes of CLS. The most common include:
- Images and Videos: Images and videos that do not have predefined dimensions can cause layout shifts during loading.
- Ads: Ads that load after the page content can cause layout shifts as they push content down.
- Custom Fonts: Custom fonts that take time to load can cause layout shifts as the page’s text may temporarily appear in a default font before switching to the custom font.
- Third-party Scripts: Third-party scripts that load after the page content can cause layout shifts if they manipulate the page’s content.
Measuring Cumulative Layout Shift (CLS)
Cumulative Layout Shift (CLS) is a web performance metric that measures the stability of a webpage’s layout during page loading. CLS measures the unexpected shifting of elements on a page that can cause a poor user experience. To measure CLS, you need to calculate the layout shift score, which is the product of the impact and distance fractions. In this article, we will discuss how to measure CLS, the importance of CLS, and tools to measure CLS.
How to measure CLS?
CLS is measured by calculating the layout shift score, which is the product of the impact and distance fractions. The impact fraction measures the viewport percentage affected by a layout shift, while the distance fraction measures the distance the affected elements have moved.
For example, if a layout shift occurs in 10% of the viewport and the affected elements have moved 100 pixels, the layout shift score would be 0.1 x 100 = 10.
The Core Web Vitals initiative introduced thresholds for CLS. A good score is 0.1 or lower, while a poor score is anything above 0.25.
Importance of CLS
The importance of CLS lies in its impact on user experience. A high CLS score means that the layout of a page is unstable, causing elements to shift during loading, which can distract and confuse users. This, in turn, leads to higher bounce rates and a decrease in user engagement. As a result, Google has made CLS a part of its Core Web Vitals, a set of user-focused metrics that measure the overall web experience.
Tools to measure CLS
There are several tools you can use to measure CLS, including:
- Google PageSpeed Insights: This tool provides insights into improving your website’s speed and user experience, including CLS.
- Lighthouse: This open-source tool audits web pages for performance, accessibility, and other best practices. It also measures CLS.
- WebPageTest: This tool measures the time it takes to load a web page and other performance metrics such as CLS.
Google Search Console also provides a CLS report that shows you the pages on your website with the highest CLS scores. This report can help you identify the pages that need improvement and the elements causing the layout shifts.
Measuring Cumulative Layout Shift (CLS) is essential for optimizing website performance and user experience. To measure CLS, you need to calculate the layout shift score, which is the product of the impact and distance fractions. Several tools are available to measure CLS, including Google PageSpeed Insights, Lighthouse, and WebPageTest. By measuring and optimizing CLS, you can improve the stability of your website’s layout and provide a better user experience.
How to Fix Cumulative Layout Shift (CLS)
Cumulative Layout Shift (CLS) is a web performance metric that measures the stability of a webpage’s layout during page loading. A high CLS score can lead to a poor user experience, causing elements to shift during loading and potentially distracting and confusing users. This article will discuss how to fix CLS issues on your website.
How to identify CLS issues?
You can use various tools to identify CLS issues, such as Google PageSpeed Insights, Lighthouse, and WebPageTest. These tools provide information about CLS, including the affected elements and their impact on the page layout. Google Search Console also provides a CLS report that shows you the pages on your website with the highest CLS scores.
Once you have identified the pages with CLS issues, you can take the following steps to fix them:
Reserve space for elements
One of the main reasons for CLS is that the browser doesn’t reserve enough space for elements. This can cause other parts to shift when the part is loaded. To prevent this, you can explicitly reserve space for features by setting their height and width in your HTML and CSS.
Load content without affecting the layout
Another way to prevent CLS is to load content without affecting the layout. For example, you can use placeholder elements to reserve space for content, then replace them with the actual content once it’s loaded. This ensures that the layout remains stable during the loading process.
Optimize images and videos.
Large images and videos can significantly impact CLS. You can optimize their impact by compressing their size and using lazy loading to reduce their impact. Lazy loading ensures the content is loaded only when the user scrolls, reducing the overall load time and improving the user experience.
Minimize third-party scripts
Third-party scripts, such as advertising and analytics, can also contribute to CLS. To minimize their impact, you can delay their loading or load them asynchronously, ensuring they don’t block the main thread and cause layout shifts.
Test and monitor
After making changes to your website, testing and monitoring the CLS score to ensure it has improved is essential. You can use the same tools for identifying CLS issues to scan the score regularly and make further optimizations if necessary.
Fixing Cumulative Layout (CLS) issues is crucial for providing a better user experience and improving website performance. By reserving space for elements, loading content without affecting the layout, optimizing images and videos, minimizing third-party scripts, and testing and monitoring, you can significantly reduce CLS and provide a stable structure for your users.
Conclusion
Cumulative Layout Shift (CLS) is an essential web performance metric that measures the stability of a webpage’s layout during page loading. A high CLS score can lead to a poor user experience, causing elements to shift during loading and potentially distracting and confusing users. In this article, we have discussed CLS, how to measure it, and how to fix it.
To fix CLS issues on your website, you need to identify the pages with high CLS scores and take steps to optimize them. This includes reserving space for elements, loading content without affecting the layout, optimizing images and videos, minimizing third-party scripts, and testing and monitoring regularly.
By following these steps, you can significantly reduce CLS and provide a stable layout for your users, improving their experience on your website. Remember that website performance and user experience are closely related, and optimizing for one can enhance the other. By prioritizing CLS and other web performance metrics, you can provide a fast and seamless user experience, increasing engagement and conversions.
F.A.Q
How to improve cumulative layout shift?
Improving Cumulative Layout Shift (CLS) is crucial for providing a better user experience and improving website performance. Here are some ways to enhance CLS:
- Reserve space for elements: One of the primary reasons for CLS is that the browser doesn’t reserve enough space for details. To prevent this, you can reserve space for features by explicitly setting their height and width in your HTML and CSS. This will ensure the browser reserves enough room for the element before it loads, preventing other features from shifting.
- Load content without affecting the layout: Another way to prevent CLS is to load content without affecting the structure. For example, you can use placeholder elements to reserve space for content, then replace them with the actual content once it’s loaded. This ensures that the layout remains stable during the loading process.
- Optimize images and videos: Large photos and videos can significantly impact CLS. You can optimize their impact by compressing their size and using lazy loading to reduce their impact. Lazy loading ensures the content is loaded only when the user scrolls, reducing the overall load time and improving the user experience.
- Minimize third-party scripts: Third-party scripts, such as advertising and analytics, can also contribute to CLS. To minimize their impact, you can delay their loading or load them asynchronously, ensuring they don’t block the main thread and cause layout shifts.
- Test and monitor regularly: After making changes to your website, it’s essential to test and monitor the CLS score to ensure it has improved. You can use various tools such as Google PageSpeed Insights, Lighthouse, and WebPageTest to scan the score regularly and make further optimizations.
In summary, improving CLS requires reserving space for elements, loading content without affecting the layout, optimizing images and videos, minimizing third-party scripts, and testing and monitoring regularly. By prioritizing CLS and other web performance metrics, you can provide a fast and seamless user experience, increasing engagement and conversions.
What is the best cumulative layout shift?
The best cumulative layout (CLS) score is 0.0, meaning there is no layout shift during loading. However, achieving a perfect CLS score is not always possible or necessary, and a score of 0.1 or lower is considered good. A score between 0.1 and 0.25 needs improvement, while a score above 0.25 is considered poor.
Google has included CLS as part of its Core Web Vitals, a user-focused metric measuring the web experience. The Core Web Vitals initiative recommends a CLS score of 0.1 or lower for a good user experience. Websites that achieve this score will likely have stable layouts during the loading process, providing a seamless user experience.
In summary, the best cumulative layout shift score is 0.0, but achieving a score of 0.1 or lower is considered good and recommended by Google’s Core Web Vitals initiative for providing a positive user experience.
How do you resolve cumulative layout shifts?
Cumulative Layout Shift (CLS) can be resolved by identifying the root causes of the layout shift and implementing fixes. Here are some ways to resolve CLS:
- Define Image and Video Dimensions: Define the dimensions of images and videos in HTML, which will reserve the space needed for them before they load. This will prevent them from shifting the layout during loading.
- Reserve Ad Space: Reserve ad space before they load, preventing them from pushing down the page’s content and causing layout shifts.
- Load Third-party Scripts Asynchronously: Load third-party scripts asynchronously so that they do not block the page from rendering. This will prevent them from manipulating the page’s content and causing layout shifts.
- Use Placeholder Elements: Use placeholder elements that reserve space for images and videos before they load, preventing layout shifts.
- Set Dimensions for Dynamic Content: Set dimensions for dynamically generated content, such as images from a CMS, to avoid layout shifts.
- Preload Custom Fonts: Preload custom fonts to ensure they are loaded before the page content, preventing layout shifts.
- Monitor and Test: After making changes, monitor and test your website’s CLS score to ensure it has improved. You can use tools such as Google PageSpeed Insights, Lighthouse, and WebPageTest to scan the score regularly and make further optimizations.
Resolving Cumulative Layout Shifts requires identifying the root causes and implementing fixes. By defining image and video dimensions, reserving ad space, loading third-party scripts asynchronously, using placeholder elements, setting sizes for dynamic content, preloading custom fonts, and monitoring and testing, you can significantly reduce CLS and provide a stable layout for your users.
