October 1, 2026 · CTREX Team
Ads without content shifting: How CTREX helps control CLS
Ads should generate revenue, not disrupt the user's experience. When ads load with a delay and change the position of elements, content can shift unexpectedly. This behavior affects CLS (Cumulative Layout Shift), one of the Core Web Vitals metrics used to assess the visual stability of a page.
This is an important aspect for publishers: effective monetization must be combined with a high-quality user experience and good website performance.
What is CLS and why is it important?
CLS indicates how much page elements shift unexpectedly during loading. For example, a user starts reading an article, and after an ad appears, the text shifts downwards.
Such shifts can degrade the user experience, especially on mobile devices, where screen space is limited.
Ads can also cause CLS if they are not allocated space in the page structure.
How does CTREX help control layout shifts?
CTREX uses the Layout Reservation approach, reserving space for the ad container before the creative itself loads.
This allows you to pre-define the area the ad will occupy, rather than adding it to the layout after the page loads.
Stable Page Structure Reserved space reduces the likelihood that the appearance of an ad creative will unexpectedly shift text or other elements.
Better User Experience When the layout remains stable, users can more easily read content and interact with the page without sudden element shifts.
Core Web Vitals Monitoring Reducing unexpected layout shifts helps publishers improve CLS as part of overall site performance optimization.
Monetization and UX Can Work Together
It's important for a publisher to consider not only the potential revenue from an ad unit, but also how it behaves on the page.
Ads that appear unpredictably and shift content can degrade the user experience. Conversely, pre-reserved ad space allows for more seamless monetization integration.
Layout Reservation isn't the only factor determining the final CLS. Core Web Vitals are also affected by images, fonts, dynamic content, JavaScript, and other page elements.
A stable layout is the foundation of high-quality monetization.
CTREX helps publishers integrate ads so they fit seamlessly into the page structure and have a lesser impact on layout stability.
Monetization shouldn't come at the expense of user experience.
Want to optimize ad monetization with UX and performance in mind? Join CTREX.