Google Tag Manager, or GTM, is a tool that holds all the tracking code on your website in one place. Instead of asking a developer to add each new tag, your team can add it in GTM. That is powerful, but over the years many people add things and few people remove them. The result is a container full of old tags nobody understands. Some fire twice. Some fire on the wrong pages. Some send data to tools you no longer use.
A healthy GTM setup has a clear naming system, a short list of tags that each have a purpose, and notes that explain what each one does. It also uses something called a data layer, which is a tidy way for your website to hand information to GTM.
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What we do about it
Marketing teams that inherited a messy setup, agencies that manage many containers, and developers who need a clear spec.