Lesson 2 of 7

Tag Assistant Preview, In Depth

Tag Assistant (GTM's Preview) is your first stop. Most people only glance at "Tags Fired". The real value is in the other tabs.

The panels that matter

Summary / message list (left): every event in order, the gtm.js load, each dataLayer push, clicks. Click an event to inspect the state at that moment.
Tags: fired vs not fired for the selected event. If a tag didn't fire, this is where you start.
Variables: the resolved value of every variable at that event, the fastest way to catch an undefined that should hold data.
Data Layer: the accumulated dataLayer state, so you can confirm the push arrived and is shaped right.

The workflow

1Pick the event→2Tag didn't fire?→3Check its trigger→4Check the variables

When a tag won't fire: select the event you expected it on, open the tag, and read why the trigger didn't match, usually a variable resolving to the wrong value.

Key takeaway

Drive Preview from the event message list, then use Tags, Variables and Data Layer to see exactly what was true at that moment. Most "it won't fire" bugs are a variable resolving wrong.