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What is CLS and why should you fix it?

Artwork presenting a juxtaposition of two webiste layouts. The one on the left seems to be in order, the one on the right seems to be falling apart.

What is CLS?

Cumulative Layout Shift (CLS) is a critical metric for webmasters, gauging the stability of elements on a website as it loads. Imagine browsing a website on your phone in an area with poor reception, like a supermarket. You spot the link you need, but just as you’re about to click, the content unexpectedly shifts. Instead of reaching your intended destination, you’re redirected to an advertisement or an unrelated page. This phenomenon, known as layout shift, can be a significant source of frustration, wasting time and souring the user experience. Although it might seem trivial from the comfort of an office, layout shifts are particularly aggravating in mobile browsing contexts, where they’re most disruptive.

How do layout shifts occur?

Layout shifts occur due to the asynchronous loading of website elements. For instance, an element could initially display certain hight, but it’s relying on a stylesheet from another server which loads slowly. If the font size for this element is twice the default size, its height might double, pushing everything below it down the page. Similarly, an over-sized website logo can delay the page layout until it fully loads, contributing to the shift. Additionally, widgets like review aggregators can further alter the layout as they load, compounding the effect.

Why are layout shifts bad?

The impact of layout shifts extends beyond mere annoyance. For users on mobile devices, a target link could move significantly, making navigation difficult. The suggestion to wait for complete page loading is impractical in many real-world scenarios, such as checking a restaurant menu on the go. Slow mobile internet or unexpected delays can exacerbate the issue, leading to wasted time and increased frustration. This negative user experience can deter customers from engaging with a business, highlighting the importance of addressing CLS not only for user satisfaction but also for business success.

Furthermore, Google incorporates CLS into its Core Web Vitals, a set of metrics influencing search ranking. Websites with high CLS scores may suffer in search rankings, underlining the significance of optimizing for this metric.

Why do layout shifts happen?

The prevalence of layout shifts can be attributed to the modern web development landscape. With an abundance of building tools, frameworks, and libraries, creating websites has never been easier. However, the integration of various systems and the inclusion of third-party widgets can introduce compatibility issues, leading to increased CLS. These widgets, often designed for easy implementation without developer assistance, can unknowingly contribute to layout instability.

In summary

In conclusion, Cumulative Layout Shift represents a pivotal challenge in web design, impacting both user experience and website performance in search rankings. Addressing CLS is not merely a technical necessity but a critical component of providing a seamless and enjoyable online experience. As the digital landscape continues to evolve, prioritizing the stability of web content becomes essential for businesses aiming to maintain a competitive edge and foster positive engagements with their audience. By understanding and mitigating the causes of layout shifts, webmasters can enhance the usability of their sites, ensuring visitors can navigate with ease and efficiency.

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