Difference between a synchronous and asynchronous tag

In Tag Manager, there are two categories of tags — asynchronous and synchronous tag. In this article, we’ll explain how they differ.

Synchronous tag

For tags that are set to load in a synchronous manner, when a page loads a synchronous tag, it needs to wait for the tag content to load before moving on to the next content.

The page starts by loading the first tag. After the tag has been completely loaded, the page moves on the second tag. The process is then repeated for the remaining tags. For example, if we have four tags on our website, and assuming that each tag loads in 0.5 second, then the total load time of all four tags will be 2 seconds.

Synchronous tags fire and load first, before the page loads. So the content of a page won’t appear until the tag are fired.

Tip: It’s a good practice to use synchronous tags for A/B tests.

Asynchronous tag

With asynchronous tags, the browser can load all tags simultaneously. It doesn’t need to wait for a certain tag to load completely before moving to the next one. For example, if we have four tags on our website, and assuming that each tag loads in 0.5 second, then the total load time of all four tags will be 0.5 second.

Asynchronous tags improve site performance because they load faster than synchronous tags. And when used as tracking tags, they allow you to collect more accurate data because they can be placed on top of the page and load immediately when the visitor enters your website.

Tip: It’s a good practice to use asynchronous tags for tracking tags.

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