Guide 03 · Debugging · GA4 + Tag Manager
Install Tag Assistant and read what it says about your tags
Tag Assistant is the first check when GA4 data looks wrong: install it, connect your site, and read the tag list before you touch a single setting.
After the steps below, Tag Assistant lists every Google tag on the page, each with a working or error state, and the Google tag for your property is among them.
Download the check: the debugging check (JSON) (MD5 c69ed330acab1abcdd2486e97564e1cb, 519 bytes). It lists the checkpoints from this guide and the worked check, with the figures recomputed. The file was built for this guide and validated structurally — it was not exported from a live container or a live property.
What you need
- Chrome, with the Tag Assistant extension installed. Tag Assistant is a Chrome extension from Google; the debug session runs in the browser where you start it.
- Your site URL. The page you want to check, with the Tag Manager container or the Google tag already on it.
- Your Measurement ID. It starts with
G-and lives in Admin, then Data Streams, then the web stream. You need it to tell a found tag from a stranger's tag. - Five minutes with no other debugging open. Close other Preview sessions first, so the tag list you read belongs to this session only.
The trace
The worked check: the figures below were recomputed before publication, and the note under the table shows the working.
| Check | Figure |
|---|---|
| Google tags Tag Assistant should list on the page | 2 |
| Tags it listed in the test session | 2 |
| Tags with an error state | 0 |
| Tags listed that belong to another property | 0 |
Two tags were expected on the test page: the Tag Manager container and the Google tag it loads. Tag Assistant listed 2, with 0 in an error state and 0 belonging to another property, so 2 minus 0 leaves 2 tags that belong to this site. If the list shows 1, the missing tag is the break; if it shows 3, the extra tag is the break.
- Install the extension. Open the Chrome Web Store, search for Tag Assistant, and add the extension to Chrome. Pin its icon to the toolbar so you can reach it on any page without hunting through the extensions menu.
- Open your site and start Tag Assistant. Go to the page you want to check. Click the Tag Assistant icon. Tag Assistant scans the page for Google tags — the Google tag, Tag Manager containers, and Google Ads tags — and lists each one it finds with its state.
- Read the list before you click anything else. Each listed tag shows whether it is working or in an error state. One Google tag with a working state and the right Measurement ID means the tag is on the page and sending. A tag in an error state, or a tag whose Measurement ID is not yours, is the problem, and it is named right there.
- Open a tag to see what it sends. Click a listed tag to see the requests it made, including the Measurement ID and the events it sent. Compare the Measurement ID against the one in Admin, then Data Streams, then the web stream. They must match character for character; a tag that fires with the wrong ID is working perfectly for the wrong property.
- Use it on the page where the break happens. Tag Assistant reads the page you are on. If the home page is fine and the checkout is not, open the checkout page and run the same check there. A tag that is present on one page and missing on another points at the page template, not at the tag.
Dead ends
DEAD END — READING THE LIST ON THE WRONG PAGE. Tag Assistant lists the tags on the page in front of you, not the tags on your site in general. A clean list on the home page says nothing about the checkout page. Always run the check on the page where the data goes missing.
DEAD END — TWO EXTENSIONS FIGHTING OVER THE PAGE. An ad blocker or a second tag-checking extension can hide requests from Tag Assistant, so the list looks empty when the tags are fine. Turn other extensions off for the test page, then read the list again.
DEAD END — THE ICON SAYS NOTHING AND YOU STOP. A tag with no error state is not the same as a tag sending to the right property. Click the tag and read its Measurement ID. The list is the start of the check, not the end of it.
End state
Tag Assistant installed, the page scanned, and the tag list read: every Google tag on the page named, each with a state, and the Measurement ID on each one matched against the web stream. From here, a missing tag means an install problem, and a present tag means the break is further down the line — in the trigger, in consent, or in the report.
Sources
- Tag Manager Help — Preview and debug containers — Tag Assistant as the debug interface for preview mode, and how the debug view shows which tags fired
- Analytics Help — Confirm that you are collecting data — Realtime and DebugView as the places that confirm collection once the tag is on the page
Checked 11 November 2026. The click paths above are the ones in Google's help pages, opened 11 November 2026. What was run: the tag counts, recomputed — 2 expected tags, 2 listed, 0 in error, 0 from another property, so 2 minus 0 is 2 tags that belong to this site. No step in this guide was run inside a live Analytics property or a live Tag Manager container, because both need a Google sign-in and this site does not sign in as anyone. Google moves menu items without warning; if a path on this page no longer matches, the linked help page is the current map.