Synchronous vs Asynchronous Rendering, which is best and when to choose which?

This post was most recently updated on September 6th, 2021

There are a lot of parts to consider when we think about optimizing and maximizing the revenue potential of our websites. We look at the layout of our page, text content quality, type of traffic, page speed, and much more. For now, let’s focus on those factors that we can control and can resolve using the features available on Doubleclick for Publishers.

Using the Google Publisher Tag (GPT) from DFP, we can control how ads are requested or how they render on your page. When generating a GPT, there will be two modes that we can choose from that would determine the behavior of ads to content on a page when the GPT is implemented on the site. These are Synchronous and Asynchronous rendering.

What happens to a page when synchronous rendering is used?

Synchronous mode makes the content and ads load depending on the order that the browser reads them. This type of rendering is best for pages that use multi-sized ad units as the rest of the page content will load after the ad is served and adjust depending on its size, avoiding the possibility of a distorted site layout.

This is also the required mode when you’re running passback tags. In some instances that the ad didn’t return the ad request right away, the rest of the content won’t load as well which causes the user to wait. The result is a negative effect on the quality of the website experience.

What do Asynchronous tags enable us to do?

Unlike with synchronous, a user visiting pages that utilize the asynchronous mode gets to see the page content without having to wait for the page to display the whole content. The type of rendering mode loads pages independently from the ads.

It is highly recommended that asynchronous rendering and the SRA option in DFP are enabled as it yields the best page load experience and the potential to serve guaranteed roadblocks as well as advertisers that competitors won’t serve their ads simultaneously to (competitive exclusion). This is the only rendering mode that makes ad slot refresh using pub service. Refresh work.

Previously, GPT GET requests larger than 4096 bytes were not supported and were being cut short. To avoid truncation, they converted GET requests to POST request method which is now supported by asynchronous GPT tags only.

SafeFrame in DFP is enabled by default when using GPT tags and recommended over-friendly iframes. It protects the sensitive data of the site from getting accessed by external elements but does not affect data collection necessary to serve relevant ads to the site.

Both rendering modes have their advantages and disadvantages. If you prefer to give the user experience more importance, choosing asynchronous rendering could be the best option. But in case you have multisize and passback ads running in your inventory, the synchronous rendering mode should be implemented to avoid ruining your site layout.

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Kean Graham

Kean Graham is the CEO and founder of MonetizeMore & a pioneer in the Adtech Industry. He is the resident expert in Ad Optimization, covering areas like Adsense Optimization,GAM Management, and third-party ad network partnerships. Kean believes in the supremacy of direct publisher deals and holistic optimization as keys to effective and consistent ad revenue increases.