In tag managers, you can use async (asynchronous) tags or sync (synchronous) tags. In this article, we’ll explain how they differ.

Async tags

Async tags don’t slow down the page load. The browser loads all tags at once, without waiting for one to finish before moving to the next. For example, if we had four tags that each took 0.5 seconds to load, the total load time for all four would be 0.5 seconds.

Async tags are faster than sync tags and work best for collecting data. Tags in Piwik PRO are async.

Sync tags

Sync tags load before the page content and wait for one to finish before moving on to the next. The page begins by loading the first tag, and only after it’s fully loaded, proceeds to the second tag. This process continues for the remaining tags. For example, if we had four tags, each taking 0.5 seconds to load, the total load time for all four tags would be 2 seconds.

Sync tags are commonly used for A/B tests.