Cumulative Layout Shift: Understanding the Impact on User Experience

As web developers, we strive to create seamless user experiences that engage and retain visitors. However, with the increasing complexity of web pages and the rise of mobile devices, a new performance metric has emerged as a major concern: Cumulative Layout Shift (CLS). In this article, we’ll delve into what CLS is, its impact on user experience, and provide actionable tips to improve it.

What Is Cumulative Layout Shift (CLS)?

Cumulative Layout Shift (CLS) measures the total distance that visible elements on a webpage shift from their initial position due to layout changes. This can occur when:

• New content loads or becomes visible
• Images or other media are loaded and resize existing containers
• Animations or transitions cause layout adjustments

CLS is calculated by adding up the maximum distance each element shifts, then taking the average of those distances.

Why Is Cumulative Layout Shift Important?

A high CLS score indicates that users experience frustrating layout shifts, which can lead to:

1. Decreased engagement: Users may become disoriented or annoyed when content suddenly moves around.
2. Reduced conversions: A poor user experience can discourage visitors from completing desired actions (e.g., filling out forms).
3. SEO consequences: Google’s Chrome User Experience Report takes CLS into account, so a high score might negatively impact your website’s visibility.

How to Improve Cumulative Layout Shift

To minimize CLS and enhance user experience, follow these best practices:

1. Use Fixed-Width Containers

Instead of using percentage-based widths or flexbox layout methods that can cause sudden shifts, stick with fixed-width containers for consistent spacing.

2. Load Assets Asynchronously

Use techniques like lazy loading to delay the loading of images, videos, or other media until they’re about to become visible in the viewport. This reduces the likelihood of CLS.

3. Optimize Image Loading

• Use compressed images to reduce load times
• Implement image resizing and caching to minimize layout shifts

4. Prioritize Content Above The Fold (ATF)

Keep essential content above the fold, avoiding sudden layout changes that might shift ATF content.

5. Avoid Overlapping Elements

Ensure that elements don’t overlap or suddenly move when new content loads. Use white space and margins to maintain a clear layout.

6. Implement Smooth Animations and Transitions

Use animations and transitions that gradually update the layout, rather than sudden jumps.

Tools for Measuring Cumulative Layout Shift

Several tools can help you analyze and improve CLS:

• Google’s Chrome User Experience Report
• Lighthouse (an automated testing tool)
• WebPageTest (a comprehensive performance testing platform)

By understanding the impact of Cumulative Layout Shift on user experience and implementing these actionable tips, you’ll be able to create a more engaging and seamless online experience for your visitors.

Do you have any questions about CLS or want to share your own strategies for improving it? Let us know in the comments below!