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Dynamic content, CLS and page rankings

Posted by John Barton | March 15, 2023

Cumulative Layout Shift (CLS) is a metric that is part of Google’s “Core Web Vitals”. Importantly, it is used as a ranking factor for search results.

CLS is the unexpected shifting of webpage elements while the page is still downloading. The kinds of elements that tend to cause shifts are fonts, images, videos, contact forms, buttons, and other kinds of content.

Minimising CLS is important because pages that shift around can cause a poor user experience.

Personalised dynamic content and CLS

Platforms such as PureClarity show different content to different users. They work by identifying the user and then requesting the dynamic content to show for the user from a server. This means these platforms typically return content whilst the page is loading.

This can sometimes cause other content on the page to move as this dynamic content is injected into the page.

This means that the CLS metric can be impacted, which can affect page rankings.

Solving with Machine Learning

PureClarity uses machine learning to try to minimise the impact of CLS. Everytime dynamic content is shown, information about the screen size, resolution and height of the content is sent to our servers. We then use k-means clustering to find “clusters” in this data - i.e. different groups of screen sizes and the heights the content needs to be set to.

The result is a custom styling guide for the PureClarity content! Different screen sizes (i.e. mobile, tablet, web, retina etc) will have different default heights for the PureClarity elements. When the page is loaded, the height of each element is pre-set, so that when the content is loaded the content doesn’t jump.

The styling is updated daily, and is calculated for all our clients on all our plans. Not many of our competitors can claim to do this! At PureClarity we believe all our clients deserve the best experience, regardless of their plan.

One e-commerce site to benefit from this has been UKMedi - a leading UK medical supply company.

Robert Gleeson from UKMedi told us:

We were really happy when PureClarity released this update to handle CLS. We noticed an immediate positive impact on our web vitals. PureClarity are always happy to help their customers and I would recommend them to other e-commerce stores.


Showing dynamic content to customers is a great way to personalise their site experience, and helps to increase conversion rate. As you can see, it doesn’t have to affect your site's performance. Make sure you ask about CLS when you use a platform to personalise the customers site experience. Why not talk to PureClarity today to find out how we can help your site.

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