Cumulative Layout Shift: What is it and how can I improve it effectively?

Discover Cumulative Layout Shift (CLS), its impact on the user experience and tips on how to optimize this crucial factor for your business. website.

Introduction to Cumulative Layout Shift

Have you ever felt frustrated when surfing the web, because a page element changed position just as you were about to click on it? This is linked to what's known as Cumulative Layout Shift (CLS), a key factor in measuring the visual stability of a web page. In this article, we'll look at what Cumulative Layout Shift really means, and how you can improve this metric to deliver a better user experience on your site or application.

What is the Cumulative Layout Shift?

Defining the Cumulative Layout Shift

Cumulative Layout Shift is a metric that evaluates the amount of unexpected movement of page elements over time. More specifically, it measures the sum of position changes of visible elements during page loading.

Why is this important?

CLS is essential because it directly affects the user experience. A high CLS score can lead to frustrated users, who may leave your site before seeing what you have to offer. As a web professional, it's imperative to optimize this metric in order to retain your audience and improve your bottom line. conversion rate.

How is the Cumulative Layout Shift calculated?

CLS components

To understand how CLS is calculated, it's important to explore its fundamental components. CLS is calculated based on element visibility offsets. This can include:

• Images : If an image loads after text, this may cause the text to drop.
• Advertising : Advertisements that appear dynamically can also displace existing elements.
• Fonts : Loading custom fonts can cause text rendering to lag.

Calculation formula

The formula for calculating CLS is quite simple. It's based on the sum of the position shifts of the elements on the page, multiplied by the fraction of the screen the element occupies. The more space the element takes up, the greater the impact of the shift.

[ CLS = sum (impact times distance) ]

Where:

• Impact is the modified screen area.
• Distance is the element's displacement in pixels.

Performance thresholds for CLS

Understanding CLS scores

CLS scores are measured on a scale of 0 to 1. Here's how it's interpreted:

• 0 à 0.1 : Excellent. Your page offers a very stable experience.
• 0.1 à 0.25 : There are some changes, but they don't seriously affect the user experience.
• 0.25 and more : Bad. Layout changes are frequent and you should consider improvements.

Why is Cumulative Layout Shift essential for SEO?

Impact on referencing

Google has introduced Core Web VitalsA series of metrics, including CLS, to evaluate the user experience on the web. A low CLS contributes significantly to a higher ranking in search results, as it reflects a more fluid and engaging experience for the user.

User engagement

A good CLS score also promotes user engagement. Stable pages encourage visitors to spend more time on your site, thus reducing the bounce rate. This increases the chances of conversion, whether it's a purchase, registration or any other desired interaction.

How can I improve Cumulative Layout Shift?

Image and media optimization

One of the main causes of layout lag is image loading. Here's how you can optimize this:

• Image sizing : Be sure to specify the width and height of images in your HTML or CSS code. This helps the browser allocate the appropriate space before the image loads.
• Use of modern formats : Image formats such as WebP offer better compression, which can reduce loading time.

Advertising management

Advertisements are often the cause of unexpected layout shifts. Here are a few tips for dealing with this problem:

• Reserve space: Provide a fixed space for ads to prevent them from displacing page elements when they appear.
• Using the delayed loading function : Load ads after the main content is displayed, minimizing the risk of lag.

Fonts and dynamic content

Fonts and other dynamic elements can often cause lag. Here are some strategies for overcoming this problem:

• Using CSS : When using custom fonts, be sure to use optimized loading mechanisms and define font dimensions once and for all.
• Reduce dynamic content : Minimize content changes during page loading to prevent unexpected lags.

Tools for measuring Cumulative Layout Shift

Google PageSpeed Insights

Google PageSpeed Insights is a free tool that measures your page's performance, including CLS score. It also offers suggestions for improvement, helping you to target high-potential areas.

Lighthouse

Lighthouse is another tool developed by Google, offering a comprehensive performance audit. It provides precise indications of CLS and other key metrics, as well as an evaluation of accessibility and SEO.

Chrome DevTools

For developers, Chrome DevTools offers advanced features for monitoring CLS in real time. You can observe your page's loading behavior and identify problematic elements.

Conclusion

Mastering the Cumulative Layout Shift is essential to optimizing not only the user experience, but also your site's SEO. By optimizing your images, managing ads appropriately and using fonts strategically, you can significantly improve this metric.

If you're experiencing difficulties or would like support in optimizing your website, you can call on DualMedia. With recognized expertise in application development and website design, the agency can help you achieve your goals. objectives digital. Take advantage of quality know-how to excel in these areas of Cumulative Layout Shift.