A tag that does not fire rarely explains itself. "Not fired" can mean the wrong event, a false condition, a blocking trigger, a paused tag or a consent setting. A tag marked as fired can still send the wrong value. Preview mode answers these questions for one action at a time, and a container export shows how the pieces connect.
Write down what should happen before you test
Open the container, stay in the Workspace tab and click Preview. Google's Preview mode guide describes the rest: Tag Assistant opens, you enter the site URL and click Connect, then you return to Tag Assistant after the site shows Connected. If the debug parameter breaks the site, untick "Include debug signal in the URL". The debug interface is visible only in the browser that started it and to people you share the session with, not to regular visitors.
Preview runs the workspace you are editing, so you can test before publishing. To check what an older version did, start Preview from that version under Versions.
Before you click anything on the site, write four expectations. Take a hypothetical report page with a CSV download button:
- Action: click the CSV button once.
- Event:
csv_exportappears in the timeline. - Tag: the GA4 event tag for the export fires on that event.
- Value:
report_typeismonthlyfor the monthly report.
Without this list, it is easy to accept whatever Preview shows. A surprising result only stands out when you have stated the expected one.
