Originally posted on April 2, 2024 @ 4:50 am
Cumulative Layout Shift (CLS) is a component of Core Web Vitals, a collection of metrics Google uses to evaluate a user’s experience on a webpage. CLS specifically gauges the stability of content during the loading of a page, noting the frequency at which users encounter unforeseen layout shifts. These unexpected changes can cause frustration and confusion, detracting from the user experience. The significance of CLS lies in its ability to quantify aspects that may cause users to navigate away from a webpage, making it an essential element in website optimization.
Research and analysis of CLS are ongoing as developers and website owners aim to understand and improve their scores. Addressing CLS involves looking at how a page loads content and the sequence of loading different elements, such as images, ads, or fonts. Optimizing for CLS not only improves the user experience but is also becoming increasingly important in the field of Search Engine Optimization (SEO), as it is one of the factors that can influence a website’s ranking on search engine results pages (SERPs).
Key Takeaways
- Cumulative Layout Shift measures the visual stability of a website during loading.
- Improving CLS is essential for enhancing user experience and website performance.
- CLS optimization can positively influence a site’s search engine rankings.
Understanding Cumulative Layout Shift
In our exploration of web performance metrics, we recognize Cumulative Layout Shift (CLS) as a critical factor for ensuring a smooth and enjoyable web experience.
Defining CLS
Cumulative Layout Shift quantifies the unexpected movement of page elements while the page is still downloading. When a visible element, like an image or a button, changes its position from one rendered frame to the next, we experience what is known as a layout shift. For a more comprehensive assessment, CLS measures the sum total of all individual layout shift scores for every unexpected layout shift that occurs during the entire lifespan of the page.
The Impact of CLS on User Experience
CLS directly impacts user experience by affecting the visual stability of a page. High CLS values indicate a lack of stability, leading to a frustrating experience as users might click the wrong button or lose their reading position. Our aim is to minimize layout shifts to provide a more predictable browsing experience, where content remains steady and reliable as a user interacts with the page.
We’ve found ensuring visual stability is not only vital for usability but also contributes to the perception of a site as smooth, responsive, and professionally designed.
Measuring Cumulative Layout Shift
Before exploring how to measure Cumulative Layout Shift (CLS), it’s essential to understand that CLS is a performance metric that quantifies how often users experience unexpected layout shifts during a page’s lifespan. Properly calculating and measuring this metric is crucial for enhancing user experience.
CLS Score Calculation
CLS score is the sum of all individual layout shift scores for every unexpected layout shift that occurs during the entire lifespan of the page. A layout shift occurs whenever a visible element changes its position from one rendered frame to the next. To calculate the layout shift score, we consider the impact fraction and the distance fraction. The impact fraction is the viewport area percentage that the shifting elements affect, and the distance fraction is the movement distance of the shifting elements relative to the viewport, measured in frame intervals. The layout shift score is the product of these two fractions:
Layout Shift Score = Impact Fraction x Distance Fraction.
Calculating this score allows us to evaluate the stability of a page’s content.
Tools for Measuring CLS
Various tools are at our disposal to measure CLS, each designed to help us understand and improve this vital web performance metric. Lighthouse and PageSpeed Insights are two prominent tools developed by Google. Lighthouse is an open-source tool that provides personalized advice for improving the quality of web pages, including diagnostics on CLS. PageSpeed Insights analyzes the content of a web page, then generates suggestions to make that page faster, incorporating data from Lighthouse.
Additionally, we use the Chrome User Experience Report to get real-world user experience insights into CLS. It provides user experience metrics for how real-world Chrome users experience popular destinations on the web, which includes measurements of CLS. These tools help us identify and rectify issues that cause layout shifts, ensuring a smooth and stable visual experience for users.
Core Web Vitals and CLS
Core Web Vitals, introduced by Google, have become essential in understanding how users experience a webpage. Cumulative Layout Shift (CLS) is a significant metric in this trio of performance measurements, specifically tracking the stability of content as a page loads.
Relation to Other Web Vitals
The suite of Core Web Vitals consists of three pillars crucial for a website’s health: Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). While LCP measures loading performance and FID assesses interactivity, CLS quantifies visual stability to prevent unexpected layout shifts during a page’s load time. Among these, LCP aims for a loading performance of 2.5 seconds or faster, and FID targets an interactivity threshold of 100 milliseconds or less.
CLS as a Ranking Factor
CLS is not only a user-centric metric but also a ranking factor for SEO as it contributes to a page’s overall user experience. A good CLS score is 0.1 or less; anything above 0.25 can negatively impact a site’s ranking in Google’s search results. Our focus should lie in maintaining this score to ensure both a seamless user experience and adherence to Google’s performance standards.
Optimizing for CLS
Cumulative Layout Shift (CLS) is a performance metric that measures how often users experience unexpected layout shifts. A low CLS score is critical for ensuring a pleasant user experience.
Optimization Techniques
We can employ several techniques to optimize for CLS:
- Images and Videos: Always include
widthandheightattributes to prevent reflows and repaints. For responsive designs, use CSS aspect ratio boxes. - Ads, Iframes, and Embeds: Reserve space explicitly, or consider lazy loading them to prevent sudden shifts.
- Fonts: Use the
font-displayCSS property to control how web fonts are displayed and avoid flashes of invisible text (FOIT). - CSS and JavaScript: Leverage CSS for animations instead of JavaScript for performance gains. Ensure that any DOM manipulations occur in batches to minimize reflows.
Avoiding Common CLS Issues
To avoid common CLS issues:
- Avoid new content insertion above existing content unless in response to a user’s action.
- Dynamic content: When adding content dynamically, reserve space beforehand or add it below the current viewport.
- Layout Instability API: Use this API to monitor and measure layout shifts to identify and troubleshoot causes.
By focusing on these strategies and techniques, we improve our website’s stability and enhance the user experience.
Developing With CLS in Mind
Cumulative Layout Shift (CLS) is a core web vital that measures visual stability, influencing how we experience webpages. As developers, we prioritize minimizing CLS to ensure a smooth and stable browsing experience for users.
Best Practices for Developers
To maintain low CLS scores, it’s crucial for us to follow best practices during development. This includes:
- Defining Size Attributes: For media like images and videos, always include width and height attributes to prevent unexpected layout shifts.
- Reserve Space for Ad Elements: Ad slots can cause layout shifts if not properly handled. Ensuring space is reserved or using placeholders can help mitigate this issue.
- Dynamic Content: For content that loads dynamically, such as comments or social media embeds, anticipate the space needed to avoid shifting surrounding content.
Using tools like the Google Search Console can aid in identifying and monitoring CLS issues.
Utilizing Stable Elements
In the context of CLS, stable elements are those that maintain their position on the page as other content may load or interact:
- Sticky Headers/Footers: These are static elements that do not disrupt the flow of the page regardless of any other dynamic content.
- Static Navigation Menus: Implementing static navigation allows users to interact with the menu without experiencing layout shifts.
By focusing on stable elements in our design and layout strategies, we uphold the integrity of the user experience and contribute to a predictable and user-friendly website.
Making CLS a central part of our development process not only aligns with best practices for creating engaging websites but also prepares our sites to meet future web standards and user expectations.
Impact of CLS on Mobile and Desktop
Cumulative Layout Shift, or CLS, impacts user experience by causing unexpected shifts of webpage elements. We’ll examine the differences in CLS effects between mobile and desktop devices, and how web developers can adapt layouts to provide a stable experience on both platforms.
Differences in CLS on Various Devices
CLS can vary significantly between mobile and desktop environments due to differing viewport dimensions and aspect ratios. Mobile devices generally have a vertical, narrow viewport, which can lead to off-screen content shifting into view unexpectedly. Desktops, with their wider aspect ratios, may encounter horizontal shifts if webpage elements resize or reposition during loading. These variations mean that a one-size-fits-all approach does not work, and site designers must account for the unique characteristics of each device type.
Adapting Layouts for Mobile and Desktop
To minimize CLS, separate layouts are often designed for mobile and desktop. Ensuring elements on a page have a defined size and space can prevent layout shifts. For example, allocating sufficient space for ad banners or images before they load can prevent elements from suddenly displacing content. Similarly, using responsive design techniques allows layouts to fluidly adjust to the changing viewport dimensions when switching from portrait to landscape orientation on mobile devices, or when resizing browser windows on desktops.
By understanding and addressing the nuances of CLS on different devices, we support a more stable, predictable browsing experience for all users.
CLS in the Field of SEO
As we unpack the impact of Cumulative Layout Shift (CLS) on SEO, it’s crucial to recognize how CLS influences page stability and, by extension, user experience—a significant factor in search engine rankings.
CLS and Page Experience
CLS is a key metric that gauges the stability of a page’s content as it loads. An optimal page experience for users is fundamental, and unexpected layout shifts can be detrimental, leading to a frustrating browsing session. We can use tools like Google Search Console to monitor and improve our site’s CLS, ensuring content remains stable and providing a seamless user interaction. High CLS scores may affect our site’s visibility, as search engines like Google take these metrics into account when determining algorithmic ranking.
The Role of CLS in Google’s Algorithms
Google algorithmically assesses web pages to provide the best match for a user’s query; within this framework, CLS has emerged as a significant factor. A higher CLS indicates poor visual stability, which Google’s algorithms may interpret as a lower quality page, potentially impeding our SEO efforts. To diagnose and optimize CLS, Ahrefs and WebPageTest are instrumental tools in our SEO toolkit, enabling us to identify elements causing the shift and rectify them. By prioritizing CLS, we focus on delivering a steadfast and engaging user experience, a cornerstone of successful SEO strategies.
Advancements and Future of CLS
In recent times, we’ve seen significant progress in addressing Cumulative Layout Shift (CLS). Our focus is now shifting towards improving user experience and site performance through innovative strategies and forecasting the future trends in this area.
Innovations in Tackling CLS
Accelerated Mobile Pages (AMP): We’ve embraced AMP to significantly enhance page stability. AMP provides a framework that preloads and pre-renders web content effectively, which reduces CLS.
- Preload Key Requests: By strategically using
preloadlinks in our head tags, we prioritize loading critical resources first to prevent layout shifts.
Core Web Vitals and BigQuery: We leverage the Chrome User Experience Report (CrUX) for real user data (RUM) with BigQuery analytics. This allows us to analyze CLS incidents deeply, comparing how our pages perform across diverse user experiences.
Predictions for CLS Evolution
We anticipate that:
- The emphasis on RUM will grow. Businesses are increasingly turning to RUM for a precise understanding of the CLS issues end users face, moving beyond lab data for actionable insights.
- A greater integration of CLS metrics into SEO will occur. With search engines valuing user experience, we predict that CLS will become a more significant ranking factor.
By remaining current with these advancements and predictions, we ensure our websites are aligned with the best practices of today and prepared for the expectations of tomorrow.
