Case studies demonstrating CLS optimization and SEO improvements

Several case studies demonstrate how optimizing Cumulative Layout Shift (CLS) can lead to significant SEO and business improvements:

• Vodafone improved their Largest Contentful Paint (LCP) by 31% through server-side rendering, reducing render-blocking JavaScript, and image optimization, resulting in an 8% increase in sales. Although this focuses on LCP, similar techniques often improve CLS as well.

• iCook achieved a 15% improvement in CLS by stabilizing ad unit sizes and pre-allocating fixed-size ad slots, along with optimizing ad script loading to prioritize header bidding and defer non-critical JavaScript. This led to a 10% increase in ad revenue.

• Redbus fixed page component slots and removed unoptimized tag insertion scripts to improve CLS, alongside optimizing third-party scripts and building microservices, which contributed to doubling mobile conversion rates and improving domain rankings.

• The Telegraph Media Group standardized ad sizes and reserved space for ad slots to prevent layout shifts caused by ads. They also improved image, header, and embed loading strategies, resulting in a 250% improvement in CLS score, increased visitor time on site, and higher ad click rates.

Common CLS optimization techniques across these cases include:

• Specifying fixed dimensions for images and ad slots to reserve space and prevent unexpected shifts.

• Preloading critical fonts and using font-display CSS properties to avoid layout shifts caused by font loading.

• Optimizing script loading, especially deferring non-critical JavaScript and prioritizing important scripts to reduce layout shifts.

• Server-side rendering of critical content to improve stability during page load.

These improvements not only enhance user experience by reducing unexpected content shifts but also positively impact SEO by improving Core Web Vitals scores, which are ranking factors in Google’s algorithm. The business impacts include higher sales, better ad revenue, increased session duration, and improved conversion rates.