How to Reduce Cumulative Layout Shift: A Practical Guide

Learn how to reduce Cumulative Layout Shift (CLS) with practical steps for image dimensions, font loading, and dynamic content to improve visual stability.

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Cumulative Layout Shift (CLS) is a Core Web Vitals metric that quantifies how often users experience unexpected layout shifts. A low CLS score, typically 0.1 or less, indicates a stable page where elements remain in place as the page loads, preventing frustrating misclicks and reading disruptions.

Key Takeaways

  • ✓CLS measures visual stability by calculating the impact and distance of shifting elements.
  • ✓Common causes include images without dimensions, late-loading ads, and web fonts.
  • ✓Optimization focuses on reserving space for dynamic content before it renders.
  • ✓Passing the 75th percentile of real-user data (field data) is the standard for a 'Good' rating.

What Makes This Different

Step-by-step guide to reduce cumulative layout shift with practical examples and expert tips.

Who This Is For

S

SEO Specialists looking to improve Core Web Vitals scores for better search visibility.

Challenge

You need effective SEO tools but struggle to find reliable data and actionable insights.

Solution

This tool provides real-time keyword data, difficulty scores, and AI-powered insights to guide your strategy.

Result

You can make informed decisions, prioritize high-value opportunities, and track your progress effectively.

W

Web Developers needing a checklist for front-end performance optimization.

Challenge

You need a checklist for front-end performance optimization but struggle to find reliable data and actionable insights.

Solution

This tool provides real-time keyword data, difficulty scores, and AI-powered insights to guide your strategy.

Result

You can make informed decisions, prioritize high-value opportunities, and track your progress effectively.

S

Site owners experiencing high bounce rates on mobile due to shifting content.

Challenge

You need effective SEO tools but struggle to find reliable data and actionable insights.

Solution

This tool provides real-time keyword data, difficulty scores, and AI-powered insights to guide your strategy.

Result

You can make informed decisions, prioritize high-value opportunities, and track your progress effectively.

S

Single-page applications where layout shifts are intentionally triggered by user interactions.

Challenge

You require specialized features that this tool doesn't provide.

Solution

Consider alternative tools or platforms specifically designed for your use case.

Result

You'll find a better fit that matches your specific requirements and workflow.

W

Websites with no dynamic content or external scripts that already maintain a 0.0 CLS score.

Challenge

You require specialized features that this tool doesn't provide.

Solution

Consider alternative tools or platforms specifically designed for your use case.

Result

You'll find a better fit that matches your specific requirements and workflow.

How to Approach

1

Define Image and Video Dimensions

Always include width and height attributes on your <img> and <video> tags. This allows the browser to calculate the aspect ratio and reserve the necessary space while the asset is still downloading.

AI Insight: Crawler data can highlight specific pages where large images lack dimensions, allowing you to prioritize high-traffic templates first.

2

Reserve Space for Third-Party Embeds

For ads, iframes, and social media widgets, use a container element with a defined min-height. This ensures that even if the ad takes a few seconds to load, the content below it doesn't jump down suddenly.

AI Insight: Analyzing SERP performance alongside CLS data can reveal if layout shifts are impacting your click-through rate on mobile devices.

3

Optimize Web Font Loading

Use 'font-display: swap' to show a fallback font immediately, or 'font-display: optional' to prevent layout shifts if the font takes too long. Preloading critical fonts can also minimize the 'Flash of Unstyled Text' (FOUT).

AI Insight: AI-driven site audits can detect if font-related shifts are isolated to specific browsers or device types, narrowing down the fix.

4

Avoid Inserting Content Above Existing Content

Unless it is in response to a user action, avoid inserting dynamic content (like banners or newsletters) at the top of the viewport. If necessary, use a placeholder or skeleton screen to occupy the space.

AI Insight: Content optimization tools can help you identify if dynamic elements are pushing down primary keyword-rich headings, potentially affecting relevancy signals.

Common Challenges

Dynamic ad sizes making it impossible to predict the required height.

Why This Happens

Reserve space for the largest likely ad size or use the most common height to minimize the shift distance.

Solution

Work with ad providers to limit the variability of ad dimensions in specific slots.

Client-side rendering causing the entire page to 'pop' in after the initial load.

Why This Happens

Use server-side rendering (SSR) or static site generation (SSG) for the main content layout.

Solution

Ensure the basic grid structure is delivered in the initial HTML/CSS.

Frequently Asked Questions

What is a good CLS score?
A good CLS score is 0.1 or lower. Scores between 0.1 and 0.25 need improvement, while anything above 0.25 is considered poor performance according to Google's thresholds.
Do user-initiated shifts count toward CLS?
No. Layout shifts that occur within 500 milliseconds of a user interaction (like clicking a 'read more' button) are excluded from the CLS calculation.
Can CSS animations cause layout shifts?
Yes, if they use properties that trigger layout changes (like 'top' or 'left'). Using CSS transforms (like 'translate') is preferred because they do not trigger layout shifts.

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