Cumulative Layout Shift (CLS) is a metric that measures unexpected layout shifts on a webpage during its loading phase. These sudden shifts can disrupt the user experience, causing frustration when content moves as users are trying to interact with it. Understanding what CLS is and how to fix it is essential for optimizing your website’s performance and ensuring a smooth user experience.
A high CLS score can negatively impact your site’s SEO and user engagement, as Google considers page experience metrics for ranking purposes. In this article, we’ll delve into what CLS is, why it’s important, and provide detailed steps and tools to help you reduce layout shifts on your website. Keep reading to learn how to improve your site’s CLS and enhance your overall web performance.
What is Cumulative Layout Shift (CLS) and Why It Is Important
Cumulative Layout Shift (CLS) is one of Google’s Core Web Vitals metrics that quantifies the visual stability of a webpage. It measures the total of all unexpected layout shifts that occur during the entire lifespan of the page. An unexpected layout shift happens when visible elements change their position from one rendered frame to the next, causing the content to move without user interaction.
CLS is crucial because sudden layout shifts can lead to a poor user experience. Imagine trying to click a button only for it to move just before you tap it, resulting in an unintended action. This not only frustrates users but can also deter them from returning to your site. Moreover, Google uses CLS as a ranking factor, meaning that a high CLS can negatively impact your site’s SEO and visibility in search results.
By optimizing for CLS, you’re not just enhancing the visual stability of your pages but also contributing to a better overall user experience and site performance. Reducing layout shifts is part of a broader strategy to improve web performance metrics, which include loading speed and interactivity. Focusing on these metrics helps ensure your site meets the standards set by search engines and provides a smooth experience for your users.
Detailed Steps to Fix Cumulative Layout Shift (CLS)
In our recent experience resolving the cumulative layout shift issue for a Toronto-based company, we observed that unexpected layout shifts were significantly affecting their user engagement and conversion rates. Their website content was frequently moving during loading, causing users to accidentally click on the wrong elements and leading to frustration. By systematically addressing the factors contributing to their high CLS score, we were able to improve their site’s performance and user satisfaction.
1. Always Include Size Attributes for Images and Videos
To prevent unexpected layout shifts caused by images and videos, always include explicit width and height attributes or use CSS aspect ratio boxes. This ensures that the browser can allocate the correct amount of space on the page while the media is loading. Without these attributes, the browser doesn’t know the dimensions of media content until it loads, causing the layout to shift when the dimensions are finally rendered. By specifying the size, you provide a placeholder that maintains the layout’s integrity, improving the visual stability of your page. Implementing these size attributes is a straightforward process that can significantly reduce your CLS score.
2. Reserve Space for Dynamic Content and Ads
Dynamic content such as ads, banners, or embedded widgets can cause significant layout shifts if not properly handled. It’s essential to reserve space in your layout for these elements, even if they load asynchronously or change dimensions. For example, you can use CSS to set a minimum height for ad containers to prevent content from suddenly moving when an ad loads. By planning for dynamic content placement, you ensure that the user experience remains consistent, and critical content stays where users expect it to be. This proactive approach helps maintain engagement and reduces frustration caused by unexpected shifts.
3. Optimize Web Fonts and Minimize Font Swapping
Custom web fonts can sometimes cause layout shifts due to font swapping or reflow when the font loads. To mitigate this, use font-display: swap or font-display: optional in your CSS to control how fonts are loaded and displayed. This practice allows text to use a fallback font until the custom font loads, preventing the text from shifting position. Additionally, consider preloading your fonts to ensure they load quickly and reduce the chance of layout shifts. Optimizing font loading not only improves CLS but also enhances overall page performance.
4. Avoid Injecting New Content Above Existing Content
Adding new content above existing content during page loading can push down other page elements, creating a layout shift. To avoid this, ensure that any new content, such as banners or notifications, is added below the fold or in reserved spaces. If you must add content above existing elements, implement it in a way that doesn’t affect the layout, such as overlaying it on top without altering the positions of other elements. By being mindful of where and how new content is introduced, you can maintain a stable layout throughout the page load.
Tools to Fix Cumulative Layout Shift (CLS)
Some of the tools we use to diagnose and resolve cumulative layout shift issues enable us to precisely identify the sources of layout instability and provide targeted solutions. Utilizing these tools helps us enhance the website’s performance and ensure a smooth user experience.
Google PageSpeed Insights
Google PageSpeed Insights is a free tool that analyzes your web page’s content and provides suggestions to improve its performance. It reports on the Core Web Vitals, including CLS, helping you identify issues causing layout shifts. By entering your URL, you receive a detailed report highlighting problem areas and recommendations. Using this tool allows you to measure your CLS score and monitor improvements as you implement fixes.
GTmetrix
GTmetrix is another valuable tool for diagnosing and fixing CLS issues. It provides detailed performance reports, including a breakdown of Core Web Vitals like CLS. GTmetrix highlights layout shift occurrences, helping you identify the elements causing instability. Its visual tools, such as Waterfall charts and Video Playback, allow you to analyze page behaviour and prioritize changes to reduce CLS. This makes GTmetrix a practical choice for web developers seeking precise and actionable insights.
Common Mistakes in Fixing Cumulative Layout Shift (CLS)
Failing to Reserve Space for Ad Elements
A common mistake in addressing CLS is failing to reserve adequate space for ad elements that load dynamically. Ads often load asynchronously and can vary in size, causing sudden shifts in content when they appear. This oversight leads to significant layout instability, negatively impacting the user experience.
This issue occurs when ad containers are not assigned fixed dimensions or placeholders. As a result, when the ad content finally loads, it pushes down or shifts existing content to make room. Since ads can be unpredictable in size, the layout shifts can be substantial and unexpected, especially on mobile devices where screen real estate is limited.
Not reserving space for ads disrupts the visual flow of the page, leading to user frustration. Users may lose their place while reading or accidentally click on elements they didn’t intend to. This not only degrades the user experience but can also decrease engagement metrics like time on the page and increase bounce rates. Moreover, it contributes to a higher CLS score, which can negatively affect your search rankings.
To avoid this mistake, always allocate predefined space for ad slots within your page layout. Use CSS to set explicit width and height for ad containers, or use aspect ratio boxes to maintain space even before the ad loads. Additionally, implement guidelines with your ad providers to ensure ads served fit within the designated spaces. This proactive sizing prevents content shifts and maintains a consistent layout, improving both user experience and CLS scores.
Neglecting to Specify Image Dimensions
Another frequent error is neglecting to specify dimensions for images and other media elements. Without defined sizes, images can cause unexpected shifts as the browser doesn’t know how much space to reserve until the image loads.
When image dimensions are not specified, the browser renders the page without allocating space for the images. Once the images load, the browser must adjust the layout to accommodate them, causing content below or around the images to shift. This can happen even with fast-loading images, as the timing can vary based on network conditions.
This oversight leads to a poor user experience, as text and other elements move unexpectedly. Users may find it difficult to read content or interact with page elements if everything is shifting as images load. It increases the CLS score, which can hurt your SEO ranking and reduce user satisfaction, potentially impacting conversion rates and return visits.
Always specify the width and height attributes in the HTML or set equivalent CSS styles for all images and media. This practice allows the browser to allocate the correct space during the initial render. For responsive designs, use aspect ratio boxes or CSS to ensure images scale properly without causing layout shifts. By doing so, you maintain a stable layout and enhance the overall user experience.
Ignoring Font Loading Optimization
Ignoring font loading optimization is a common mistake that can contribute to layout shifts. Custom fonts, when not properly managed, can cause text to reflow once the font has loaded, altering the spacing and causing content to move.
This issue occurs when the browser initially displays text using a fallback font and then swaps to the custom font once it loads. The difference in font metrics between the fallback and custom font can change the size and spacing of text elements, leading to shifts in the layout. This is known as Flash of Unstyled Text (FOUT) or Flash of Invisible Text (FOIT).
Font swapping disrupts the reading experience, as content moves or reflows unexpectedly. It can be particularly jarring for users if they are in the middle of reading or interacting with the page. Such disruptions contribute to a higher CLS score and diminish the perceived quality of your website, potentially affecting user retention and search engine rankings.
To mitigate this issue, use the font-display CSS property to control how fonts are loaded and displayed. Setting font-display: swap allows text to be displayed immediately with a fallback font, then swapped to the custom font once it loads without causing layout shifts. Alternatively, font-display: optional can be used to avoid swapping altogether if the custom font is slow to load. Preloading fonts can also ensure they load earlier in the page lifecycle, reducing the chance of layout shifts. These practices help maintain text stability and improve user experience.
Conclusion
Understanding and addressing Cumulative Layout Shift (CLS) is essential for providing a smooth user experience and maintaining strong SEO performance. Unexpected layout shifts can frustrate users, leading to decreased engagement and potentially harming your site’s reputation. Since CLS is a key metric in Google’s evaluation of page experience, optimizing for it is crucial for maintaining and improving your search rankings.
By implementing practices such as specifying dimensions for images and media, reserving space for dynamic content, optimizing font loading, and avoiding the injection of content above existing elements, you can significantly reduce layout shifts. Utilizing tools like Google PageSpeed Insights, Chrome DevTools, Lighthouse, and WebPageTest allows you to diagnose and monitor CLS issues effectively. Addressing common mistakes and following best practices ensures your website offers a stable and enjoyable experience for your users.
What We Can Offer You
At ENoptimize, we specialize in enhancing website performance by addressing critical issues like Cumulative Layout Shift. With over 10 years of experience working with businesses in Toronto and across Ontario, our team has the expertise to identify and resolve the factors that negatively impact your site’s user experience and SEO rankings. We understand the nuances of web performance optimization and are committed to helping our clients achieve a stable and engaging online presence.
We offer comprehensive solutions tailored to your specific needs, leveraging industry-leading tools and techniques to minimize layout shifts and improve overall site performance. Our approach includes a thorough analysis of your website to identify the root causes of high CLS scores, followed by the implementation of best practices and continuous monitoring. This ensures that your site not only meets but exceeds the performance standards set by search engines.
If you’re looking to enhance your website’s visibility and provide a better experience for your users, our team is here to help. Learn more about how we can improve your site’s performance and search rankings with our advanced SEO strategies.