Google Tag Assistant: how to debug your tags step by step

Google Tag Assistant is Google’s free tool for checking whether the tags on your website work correctly. Per page and per click, you see which tags fire, which don’t, which data they send and which consent status applies. That makes it the fastest way to find out why a conversion is missing, counted twice or given the wrong value. In this article you will read how to open Tag Assistant, how to read a debug session and which checks you should do at a minimum before you publish anything.

What is Google Tag Assistant?

In its help centre, Google describes Tag Assistant as a tool to “check the implementation and operation of tags on your website”. You review tags, events and data, and you can export and import debug sessions to share them with colleagues.

Tag Assistant works via the website tagassistant.google.com, with an optional Chrome extension, Tag Assistant Companion. That extension is useful for two situations that are otherwise hard to test: tags in an iframe (think of an embedded form or scheduling tool) and pop-ups or new tabs that open from your page. Still looking for the old standalone extension “Tag Assistant Legacy”? Work with the web version and the Companion extension today.

Three ways to open Tag Assistant

Via Preview in Google Tag Manager

This is the route you will use most often. In your GTM workspace, click Preview at the top right. According to the GTM documentation, Tag Assistant then opens in a new tab, you enter your site’s URL and click Connect. Your site opens in a new window with the message “Connected” at the bottom right. Everything you do on the site after that appears in the debug view.

Via tagassistant.google.com

On tagassistant.google.com, choose Add domain and enter your URL. Tag Assistant adds a debug parameter (_dbg) to the URL and follows your session. This also works on sites where you have no GTM access, for example to quickly look at a new client’s Google tag.

Via GA4 DebugView

A tag that fires is not yet an event that GA4 processes correctly. That is why you also check in GA4 under Admin > DebugView. According to Google’s explanation of DebugView, sessions from Tag Assistant or preview mode appear there automatically. Note: events are not visible in DebugView if consent mode is active and the test user did not give consent. So accept the cookies in your test window, or deliberately test the declined route as well.

Reading a debug session: step by step

1. Start with the timeline on the left

On the left you see a timeline with every moment GTM records: the container loading, “Consent Initialization”, “Initialization”, “Container Loaded”, “DOM Ready”, “Window Loaded”, and after that every click, form submission or custom event from your data layer. Click a moment to see what happened at that point. Now perform the action you want to test, for example submitting a form, and look for the matching moment.

2. Check Tags Fired and Tags Not Fired

For each moment, Tag Assistant shows which tags fired and which didn’t. If your conversion tag is listed under “Not Fired”, click it: you will see which trigger condition was not met. If it fires on every page instead of only after the submission, your trigger is too broad.

3. Look at the data in Variables and Data Layer

On the Variables tab you see the value of every variable at that moment: the conversion value, the form ID, the page. On the Data Layer tab you see exactly what your website passed on. If the value is right in the data layer but not in the variable, the error is in GTM. If it is already missing in the data layer, the error is on the website. Read more about that structure in the data layer explained.

4. Check the consent status

On the Consent tab you see the default status and the updated status per consent type, such as ad_storage and analytics_storage. Test at least two scenarios: everything accepted and everything declined. In the second case, advertising tags must not set cookies. How consent mode fits together is explained in consent mode v2 for Google Ads.

5. Check receipt in the platform

Then go to the platform itself: GA4 DebugView, the conversion diagnostics in Google Ads, the test events in Meta Events Manager. Only when the event arrives there with the right parameters has your test succeeded.

6. Share the session

Does a developer or colleague need to take a look? In Tag Assistant, choose More Actions and then Share to share a preview link. You can also export a session, which is handy for showing a problem later.

Checklist: what do you test per platform?

Common mistakes we find with Tag Assistant

• A conversion that fires on every page view. Often a trigger on “All Pages” or on a thank-you page that reloads via the back button.
• Two GA4 configurations at once. A hard-coded Google tag in the theme plus a tag in GTM: every page view counts twice.
• Forms in an iframe. Without the Companion extension you don’t see them, and without separate measurement they don’t count.
• Test traffic in your numbers. At Tryve, the audit revealed that test hits counted as real conversions and so ended up in the Google Ads bidding strategy. Filter internal and test traffic in GA4 and preferably test conversions in a separate environment.
• Forgetting a successful test after a form update. At Suivo, a form update silently stopped lead measurement without any error message. We found the cause through a root cause analysis in GTM Preview.

Read more patterns in common mistakes in Google Analytics tracking.

Debugging server-side containers

If you work with server-side tagging, your server container has its own preview mode. There you see, per incoming request, which client picked it up, which tags fired and which outgoing requests left for GA4, Google Ads or Meta, with their status code. Test the web container and the server container together: an event that leaves the browser correctly can still fail in the server.

When is Tag Assistant not enough?

Tag Assistant shows one session in one browser. It does not tell you whether your numbers are right over a month, whether GA4 and Google Ads count the same number of leads, or whether your CRM and your advertising platforms line up. For that you need a broader check. A tracking audit puts your tags, consent, conversions and the differences between platforms side by side and gives you a prioritised list of what to fix first. Also read why conversions in Google Ads and GA4 differ.

Frequently asked questions

Is Google Tag Assistant free?

Yes. Tag Assistant on tagassistant.google.com and the Companion extension are free. You need a Google account and, for GTM preview mode, access to the container.

Why doesn’t Tag Assistant show my site as “Connected”?

Usually something is blocking the connection: an ad blocker, a cookie banner that prevents the container from loading, a redirect to a different URL or a pop-up blocker. Try a private window without extensions, and check whether the GTM snippet is on the page.

Why don’t I see my events in GA4 DebugView?

Often because consent was declined in your test session: in that case events are not visible in DebugView. Also check whether you are looking at the right GA4 property and whether the debug session is still active.

Does Tag Assistant also work for the Meta pixel or LinkedIn?

Tag Assistant shows whether the tag fires in GTM, including for Meta or LinkedIn. Whether the platform receives the event correctly, you check in that platform’s own tools, such as the test events in Meta Events Manager.

Can I use Tag Assistant without Google Tag Manager?

Yes. Via “Add domain” on tagassistant.google.com you can also debug a site that uses the Google tag directly. You then see the Google tag and the events, but not the GTM-specific tabs such as triggers.

Have your tags checked

Do you see things in Tag Assistant that you can’t explain, or do you want to be sure every conversion is right before you invest more budget? With a tracking audit we check your entire setup, and our tracking specialist fixes what is wrong. For the basics of your container, also read our article on Google Tag Manager. Get in touch if you want to discuss it straight away.