📈 What is Cumulative Layout Shift (CLS)?
Cumulative Layout Shift (CLS) is a web performance metric that measures the visual stability of a webpage. It quantifies how unexpected layout shifts impact user experience as the page loads.
⭐ Why is CLS Important?
CLS is crucial because sudden layout shifts can disrupt user interaction, lead to poor user experience, and negatively affect conversion rates. A good CLS score enhances site usability, which is a significant factor in SEO and user retention.
⚙️ How Does CLS Work?
- CLS measures how much visible content shifts within the viewport.
- The metric calculates layout shifts by monitoring movement between two rendered frames.
- A lower CLS score indicates a more stable page, improving user experience and potentially boosting SEO.
📌 Examples of Layout Shifts
- An image without dimensions pushing text down as it loads.
- Late-loading ads causing page content to shift unexpectedly.
- Dynamic, network-driven content resizing, causing button movement.
✅ Best Practices to Improve CLS
- Always specify size attributes for images and videos.
- Avoid inserting content above existing content without proper space.
- Reserve ample space for ads and embeds to prevent layout shifts.
- Use CSS aspect ratio boxes for responsive media content.
⚠️ Common CLS Mistakes to Avoid
- Not defining dimensions for media elements causing shifts.
- Using late-injected elements on a web page.
- Failure to anticipate user interaction-driven content shifts.
🛠️ Tools for Analyzing CLS
- Google PageSpeed Insights for CLS measurement and suggestions.
- Lighthouse in Chrome DevTools offers detailed CLS diagnostics.
- WebPageTest for comprehensive CLS and performance metrics.
📊 Quick Facts About CLS
- CLS is a part of Google's Core Web Vitals for assessing user experience.
- A CLS score of 0.1 or less is considered good by Google standards.
- Layout shifts typically result from images and ads loading asynchronously.
❓ Frequently Asked Questions About CLS
What is considered a good CLS score?
A good CLS score is 0.1 or less, indicating minimal visual disruption.
Does CLS affect SEO rankings?
Yes, CLS is included in Core Web Vitals, impacting page experience signals used by Google to rank pages.
Can CLS changes occur after initial page load?
Yes, if asynchronous or dynamically-loaded content causes shifts post initial loading.
🔍 Related Web Metrics
📚 Learn More About CLS
📝 Key Takeaways
- CLS measures the visual stability of a web page as it loads.
- A good CLS score is vital for user experience and SEO.
- Implement best practices like size attributes for media to reduce CLS.