Cumulative Layout Shift (CLS)

Cumulative Layout Shift (CLS) Interpretation

High CLS values indicate poor visual stability, which can frustrate users and lead to abandonment. Low values suggest a seamless experience, enhancing user trust and engagement. Ideal targets for CLS are below 0.1 for optimal performance.

• <0.1 – Excellent user experience; minimal layout shifts
• 0.1–0.25 – Acceptable; monitor for potential issues
• >0.25 – Poor experience; urgent remediation needed

Common Pitfalls

Many organizations overlook the impact of layout shifts on user experience, leading to higher bounce rates and lost revenue opportunities.

• Neglecting to optimize images and media can cause unexpected shifts during loading. Large files or incorrect dimensions lead to layout instability, frustrating users and impacting engagement.
• Failing to reserve space for dynamic content results in layout shifts as elements load. This can confuse users, especially if critical buttons or links move unexpectedly.
• Overusing third-party scripts without proper management can introduce variability in loading times. These scripts may not load consistently, causing layout shifts that disrupt user interactions.
• Ignoring mobile responsiveness can lead to significant CLS issues. Elements that shift between desktop and mobile views can alienate users and degrade overall experience.

Improvement Levers

Improving CLS requires a focused approach to web design and development practices.

• Specify dimensions for images and videos to prevent layout shifts during loading. This ensures that the browser allocates the correct space, enhancing visual stability.
• Implement font loading strategies to minimize shifts caused by text rendering. Using font-display: swap can improve perceived performance and reduce layout instability.
• Limit the use of dynamic content that alters layout unexpectedly. Consider using placeholders or skeleton screens to maintain layout integrity during loading.
• Regularly audit third-party scripts and their impact on layout shifts. Removing unnecessary scripts or optimizing their loading can significantly enhance CLS performance.

Cumulative Layout Shift (CLS) Case Study Example

A leading e-commerce platform faced challenges with high CLS, resulting in decreased user engagement and increased cart abandonment. With CLS values averaging 0.35, the company recognized the need for immediate action to enhance user experience and drive sales. They initiated a project called "Stability First," focusing on optimizing their website's loading performance and visual stability.

The team began by analyzing user behavior data to identify the most problematic areas causing layout shifts. They prioritized optimizing images and videos, ensuring all media had defined dimensions. Additionally, they implemented a content delivery network (CDN) to speed up asset loading times, reducing the likelihood of shifts during page rendering.

Within 6 months, the e-commerce platform reduced its CLS to 0.08, significantly improving user experience. The changes led to a 20% increase in conversion rates and a notable decrease in bounce rates. Customers reported higher satisfaction levels, and the company saw a positive impact on overall revenue. The "Stability First" initiative not only improved CLS but also reinforced the importance of user-centric design in their digital strategy.