CLS (Cumulative Layout Shift)

# CLS (Cumulative Layout Shift)

CLS, or Cumulative Layout Shift, measures the visual stability of a webpage by quantifying unexpected layout changes that occur during loading.

Understanding CLS in Depth

CLS is part of the Core Web Vitals, a set of metrics focused on user experience. It specifically captures how often and how much a page's elements shift unexpectedly, which can disrupt user interactions. Variations in CLS often arise from factors like images without defined dimensions, dynamically injected content, or ads that load after the main content. Teams may adapt their approach to CLS by prioritizing the allocation of space for elements or implementing best practices for loading content to minimize shifts.

Connection to UX Practices

CLS is closely related to overall user experience design, particularly in terms of usability and accessibility. A high CLS score can lead to frustration and confusion for users, negatively impacting their perception of a product. Incorporating CLS considerations into design frameworks, such as responsive design or mobile-first strategies, can enhance the stability and usability of a site.

Practical Insights

Always specify dimensions for images and videos to prevent shifts.

Reserve space for ads or dynamic content to minimize layout changes.

Test pages with different devices and network conditions to identify potential layout shifts.

Monitor CLS regularly as part of performance audits to ensure a stable user experience.

CLS (Cumulative Layout Shift) helps ensure a stable user experience by minimizing unexpected layout changes during page load.

Measure CLS values using performance testing tools to identify layout shifts.

Analyze user interactions to determine how layout shifts affect usability.

Optimize images and video elements to load with defined dimensions, reducing shifts.

Review third-party scripts and ads that may cause layout instability.

Implement best practices for loading fonts to prevent text shifts.

Test across different devices and browsers to ensure consistent performance.

Correctly applying the term "CLS (Cumulative Layout Shift)" enhances user experience by providing a more stable and engaging interface. This leads to improved usability for users, streamlined processes for teams, and better performance metrics for the business.

Reduces user frustration by minimizing unexpected shifts in layout.

Enhances overall site performance, leading to higher user satisfaction.

Supports better decision-making by providing clear metrics for design improvements.

Improves accessibility by ensuring content remains stable during loading.

Facilitates smoother workflows for design and development teams, promoting collaboration.

During a recent project, the product team at a popular e-commerce website noticed an increase in user complaints about a frustrating shopping experience. Customers reported that items would shift unexpectedly while they were trying to add products to their cart. To address this, the product manager organized a meeting with the designer, researcher, and engineer to investigate the issue further.

The researcher conducted usability tests and found that these unexpected layout shifts, measured by CLS (Cumulative Layout Shift), were causing users to accidentally click on the wrong items. The designer reviewed the website’s layout and identified that the issue primarily stemmed from images loading after text and buttons. This led to a cascading effect, where users would lose their place on the page, impacting their overall shopping experience.

To resolve the problem, the engineer implemented a solution that involved reserving space for images before they loaded. This adjustment helped stabilize the layout, minimizing shifts and improving the CLS score. After deploying the changes, the team monitored user feedback and found a significant decrease in complaints related to layout shifts, resulting in a smoother and more enjoyable shopping experience for customers.

Cumulative Layout Shift (CLS) is particularly useful during the design and optimization stages of web development. It helps ensure a stable visual experience for users as pages load.

Discovery: Identify potential layout issues by analyzing existing pages for unexpected shifts during user testing.

Design: Ensure that design elements are properly sized and positioned to reduce the likelihood of layout shifts when content loads.

Delivery: Validate that the final product maintains a stable layout across different devices and screen sizes before launch.

Optimization: Monitor and improve CLS scores post-launch to enhance user experience and decrease bounce rates.

Testing: Conduct A/B testing to compare layout stability between different design options and determine the best user experience.

Feedback Analysis: Review user feedback related to layout issues to identify areas needing improvement in future iterations.

Teams can struggle with Cumulative Layout Shift (CLS) due to its technical nature and the complex interplay of design and performance factors. Misunderstandings about what constitutes a layout shift can lead to neglecting critical aspects of user experience. Additionally, organizational constraints and data limitations can hinder effective monitoring and improvement efforts.

Misunderstanding layout shifts: Teams may not recognize all elements that contribute to CLS.

Hint: Educate team members on what causes layout shifts, such as images without defined dimensions.

Inconsistent measurement: Different tools may report varying CLS values, leading to confusion.

Hint: Use a standardized tool for measuring CLS and ensure consistent reporting practices across teams.

Design trade-offs: Striving for low CLS may conflict with creative design choices, potentially stifling innovation.

Hint: Balance design aesthetics with performance by considering user experience in the design phase.

Limited visibility on user experience: CLS may not fully capture the user's perception of layout stability.

Hint: Complement CLS metrics with user testing to gather qualitative feedback on layout changes.

Organizational buy-in: Getting stakeholders to prioritize CLS can be challenging amidst competing metrics.

Hint: Present CLS data alongside its impact on user engagement and conversion rates to gain support.

Dynamic content issues: Websites with dynamic content may face more frequent layout shifts, complicating stabilization efforts.

Hint: Implement placeholders or skeleton screens for dynamic content to reduce unexpected shifts.

Cumulative Layout Shift (CLS) can be managed and measured using various methods and tools to enhance user experience by minimizing unexpected layout changes.

Methods

Design System Implementation: Establish a design system to maintain consistent spacing and element sizes across the interface.

Preloading Key Resources: Use preloading techniques to ensure critical resources load first, reducing layout shifts.

Properly Size Media: Define explicit dimensions for images and videos to prevent layout shifts when they load.

Avoid Inserting Content Above Existing Content: Ensure new content is added below existing content to prevent shifts in the layout.

Use CSS for Layout Stability: Apply CSS properties like `min-height` to elements to reserve space and avoid layout shifts.

Tools

Performance Monitoring Tools: Use tools that track web performance metrics, including CLS, such as Google Lighthouse or WebPageTest.

Browser Developer Tools: Leverage built-in browser tools to analyze layout shifts during page load.

Web Vitals Extension: Utilize browser extensions that monitor Web Vitals, including CLS, in real-time.

UX Testing Platforms: Employ UX testing platforms that measure user experience metrics and provide insights on layout stability.