Conquering CLS: A Detailed Tutorial on Optimizing Cumulative Layout Shift
Cumulative Layout Shift (CLS) can be a frustrating foe for web developers, causing annoying jumps and shifts in content that disrupt user experience. But fear not, for with the right tactics, you can tame this beast and ensure your website delivers a smooth and seamless journey for your visitors.
First, Understand the Enemy:
- What is CLS? CLS measures the total distance an element moves unexpectedly on a page after it first paints. A high CLS score indicates a jittery and unstable layout, impacting user engagement and SEO.
- Why is it important? Google Core Web Vitals considers CLS a crucial ranking factor, meaning a high score can hurt your search visibility. Additionally, a poor user experience due to CLS can lead to higher bounce rates and lost conversions.
Now, Let’s Battle CLS:
1. Identify the Culprits:
- Use DevTools: Chrome DevTools’ “Layout Shift” tab reveals which elements are causing the most CLS. Analyze the timestamps and inspect the element styles to pinpoint the source of the shifts.
- WebPageTest: This tool provides a CLS score and detailed breakdown of layout shifts, helping you identify specific elements and events contributing to the problem.
2. Implement the Cure:
- Preloading Resources: Preload fonts, images, and other large media files to prevent them from causing layout shifts when they load later. Use
<link rel="prefetch">tags to prioritize critical resources.
- Set Dimensions: Define explicit dimensions (width and height) for images, videos, and embeds to reserve space in the layout and prevent content from shifting when they load.
- Optimize CSS: Avoid using relative units like
%for element sizes, and instead use fixed units like
emfor predictable layout behavior.
- Optimize Fonts: Use font-display: swap to prevent FOUC (flash of unstyled content) and ensure a smooth transition to the desired font.
3. Monitor and Maintain:
- Track CLS Score: Regularly monitor your website’s CLS score using tools like Lighthouse or PageSpeed Insights to track progress and identify any regressions.
- Continuous Improvement: Optimizing CLS is an ongoing process. Keep testing and refining your strategies to ensure a consistently stable and user-friendly layout.
- Use CSS Grid or Flexbox: These layout methods offer more control over element positioning and can help prevent layout shifts.
- Minimize FOMO: Avoid using “above the fold” content that depends on slow-loading elements, as this can lead to CLS.
- Test on Different Devices: Ensure your optimizations work across various screen sizes and devices to provide a consistent experience for all users.
By following these steps and staying vigilant, you can conquer CLS and create a website that delivers a smooth, delightful experience for your visitors, boosting your SEO and user engagement in the process. Remember, a stable layout is a happy user, and a happy user is a loyal customer!