Understanding CLS: The Key to Optimizing Your Website’s Visual Stability

Marketing Mishrag January 08, 2025

Introduction

Cumulative Layout Shift (CLS) is a critical metric in Google's Core Web Vitals that measures a website's visual stability. A high CLS score can frustrate users by causing unexpected shifts in content, leading to a poor user experience and lower rankings in search engine results.

In this blog, we’ll dive into what CLS is, why it matters, and how you can optimize your website to achieve a low CLS score.

What is CLS?

Cumulative Layout Shift (CLS) measures the total sum of all unexpected layout shifts that occur while a web page is loading or interacting. A layout shift happens when visible elements, like images, buttons, or text, move unexpectedly as the page loads.

Google defines CLS as follows:

  • Good CLS Score: Less than 0.1
  • Needs Improvement: Between 0.1 and 0.25
  • Poor CLS Score: Greater than 0.25

Why is CLS Important?

  1. User Experience: Unexpected shifts disrupt the user’s ability to read or interact with content, leading to frustration.
  2. SEO Rankings: CLS is part of Core Web Vitals, a ranking factor in Google’s algorithm. A low CLS score boosts your chances of ranking higher.
  3. Conversions: A stable layout improves user trust, increasing the likelihood of conversions.

Common Causes of Poor CLS

  1. Images Without Dimensions: Images that lack defined width and height attributes can cause shifts as the browser loads them.
  2. Ads and Embeds: Third-party ads or widgets without proper space allocation can unexpectedly push content.
  3. Dynamic Content: Late-loading elements, such as pop-ups or banners, can shift other content.
  4. Web Fonts: Fonts that load late can cause text to reflow, affecting the layout.
  5. Lazy Loading Without Placeholder: Lazy-loaded images and videos can shift content if placeholders aren’t used.

How to Measure CLS

  1. Google PageSpeed Insights: Enter your URL to get a detailed report, including your CLS score.
  2. Lighthouse in DevTools: Use Chrome’s Developer Tools to analyze layout shifts on your site.
  3. Web Vitals Extension: A Chrome extension that provides real-time metrics, including CLS.
  4. Google Search Console: Monitor Core Web Vitals reports for site-wide CLS issues.

How to Optimize CLS

1. Define Image and Video Dimensions

  • Always specify the width and height attributes for images and videos.
  • Use responsive images to adapt to various screen sizes without causing shifts.

2. Reserve Space for Ads and Embeds

  • Allocate specific areas for ads and third-party content to prevent unexpected movements.
  • Use CSS to define fixed dimensions for embedded elements.

3. Use Font-Display: Swap

  • Implement font-display: swap; in your CSS to ensure text remains visible while custom fonts load.
  • Use font subsets to reduce loading time.

4. Avoid Injecting Late Content

  • Ensure that banners, pop-ups, or dynamically loaded content don’t push existing elements.
  • Pre-load critical resources and scripts to avoid delays in rendering.

5. Add Placeholders for Lazy-Loaded Media

  • Use placeholders or skeleton loaders to maintain layout stability until the media is fully loaded.
  • Tools like object-fit can help maintain aspect ratios for media elements.

6. Test on Real Devices

  • Use tools like BrowserStack or physical devices to test your site’s CLS performance under real-world conditions.

Tools to Improve CLS

  1. Google PageSpeed Insights: Identify specific layout shifts and get optimization suggestions.
  2. Lighthouse: Run audits directly in your browser for detailed CLS insights.
  3. WebPageTest: Analyze layout stability across different devices and browsers.
  4. Ahrefs or SEMrush: Monitor CLS as part of an overall SEO performance report.

Benefits of a Low CLS Score

  • Improved User Satisfaction: A stable layout keeps users engaged and happy.
  • Higher SEO Rankings: Google rewards sites with excellent Core Web Vitals metrics, including CLS.
  • Increased Conversions: A seamless experience boosts user trust and conversion rates.

Common Mistakes to Avoid

  1. Using Unoptimized Images: Forgetting to define dimensions can lead to shifts.
  2. Neglecting Mobile Testing: Mobile devices often experience higher CLS due to dynamic layouts.
  3. Ignoring Core Web Vitals Reports: Overlooking CLS metrics in Google Search Console can result in missed opportunities.

Conclusion

Cumulative Layout Shift (CLS) is more than just a metric; it’s a reflection of your website’s user experience. By addressing layout shifts, defining dimensions, and reserving space for dynamic elements, you can provide a seamless browsing experience that keeps users engaged and improves your SEO performance.

Start optimizing your CLS score today and stay ahead in the ever-evolving digital landscape!

Have questions or tips for optimizing CLS? Share them in the comments below!

Marketing Mishrag

Posted by Marketing Mishrag

Marketing Mishrag stands as a beacon of innovation and expertise in the ever-evolving world of digital marketing. With a commitment to excellence and a deep understanding of market dynamics, Marketing Mishrag provides cutting-edge solutions tailored to elevate your brand’s online presence. From crafting impactful strategies to executing data-driven campaigns, Marketing Mishrag is your trusted partner in navigating the digital landscape with precision and creativity.

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