In Tag Manager, you can use async (asynchronous) tags or sync (synchronous) tags.
Async tag
Async tags don’t interfere with loading page content. The browser can load all tags at the same time and it doesn’t 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.
Async tags load faster than sync tags and are better for collecting data. Most of tags in Piwik PRO are async tags.
Note: To run async tags you need to install the basic container on your site or app. Read more
Sync tag
Sync tags load before the page content loads. They also 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.
Sync tags are often used to run A/B tests.
Note: To run sync tags you need to install the additional container on your site or app. Read more