Google Tag Manager. The thing that makes lives of marketers and web analysts easier. But the purpose of this blog post is not to convince you to start using it (I have another one which explains all GTM benefits). Today, I assume that you have already decided to give Tag Manager a chance (or maybe even used it once or twice). In this blog post, I’ll show you how to check if Google Tag Manager is working properly.

There are several ways to do so but keep in mind that these tips are not alternatives of each other. If possible, you should use them all or at least half of them.

#1. Enable Preview and Debug mode

This 1st technique to check if Google Tag Manager is working is to enable Preview and Debug (P&D) mode. To do so, click Preview button in the top right corner of your GTM interface (near Submit button).

Enable Google Tag Manager Debug Mode

After you enable P&D mode, a large orange notification banner will appear.

Google tag manager preview notification

Now, navigate to the site where the Google Tag Manager container code is implemented, refresh the page and a debug console window will appear at the bottom of your browser, showing detailed information about your tags, including their firing status and what data is being processed.

This console window will appear only on your computer as you preview the site, and is not visible to your other website visitors.

Google Tag Manager Debug Mode

As long as you continue navigating your site and see the Preview and Debug console at the bottom of your screen, that’s a good sign.

I’ve published a detailed guide which explains what the Preview and Debug mode is and how you can make use of it.

Is the P&D Mode not showing up? Read the guide on how to fix it.


#2. Use Google Tag Assistant

Tag Assistant is of one the top Chrome extensions for Google Tag Manager, a very useful tool in testing and debugging your implementation. Not only does it help with troubleshooting of Google Tag Manager, but also Google Adwords, Analytics, and DoubleClick implementation can be easily verified.

One of the most powerful features within the tool is recordings. This allows you to “record” a browsing session and produce a report on all of the hits being sent through and even how they will potentially show up within Google Analytics.

  1. After you install the extension, click the Tag Assistant icon in your browser.
  2. Enable the Tag Assistant and refresh your browser.
  3. Look at the status of the Google Tag Manager container. If you have yellow or red, there are problems with your installation. Click on the icon to further reveal what the problem is.

Google Tag Assistant

Your aim is to see a green tag with a smiley face, just like in the screenshot below.

Google Tag assistant - Success


#3. Leverage Screaming Frog

Another way of how Google Tag Manager implementation might be broken is when GTM container code is not added to all pages of a website. There are many reasons why things like this happen:

  1. The Content Management System is terrible and buggy.
  2. The website is using a lot of different page templates and there is no easy way to update them all at once.
  3. The developer is inexperienced, etc.

My point is that things happen and you need to be prepared for that. One of the ways how you can check whether Google Tag Manager code is added to all pages is to use a web crawler.

Screaming Frog is a solution which is especially popular among SEO professionals who want to check what’s happening on their clients’ websites. How is it related to GTM? You could configure it to crawl the entire website and look for in website’s source code. This URL is used by Google Tag Manager container.

In Screaming Frog’s application, go to Configuration > Custom > Search and enter the following condition:

Does not contain

Enter the URL of the website you wish to check and hit Start button.

Screaming frog

That’s it! As the crawl progresses, you’ll be able to see the full URLs of the pages where your GTM container code is missing. Your next step is obviously to add the tracking code to those pages or ask a developer to do that.

Google Tag Manager Course - Learn More

#4. Chrome’s developer tools

Another way how to check if Google Tag Manager is working is to dive deeper into developer’s zone. We’ll need Chrome’s developer tools here (other browsers have tools as well, but Chrome is the browser of my choice that’s why I’ll give it more attention).

On Mac, you can access Developer tools through the View menu.

Chrome developer tools on Mac

On Windows, click CTRL + Shift + I.

You will notice that an entire console is enabled at the bottom of your screen with several options. There are two tabs you should be interested in the most, Console and Network.

Developer tools on Windows

First of all, click Console and start navigating the website and keep looking for errors. If none occur, great! Otherwise, if you see a warning or an error and it contains keywords like Google Tag Manager, gtm.js, etc., this means that something’s not right with your implementation.

Discuss that with a developer, ask on GTM or Stack Overflow forums, or just google, maybe others face similar issues and have come up with a solution.

By the way, if you spot this error:

don’t worry, I have a quick solution for it, read this blog post.

Now, let’s go to the Network tab. You will also notice that it’s completely blank (or contains way too little information). This is because you will need to refresh your browser in order for this information to be populated. Refresh the browser and start seeing some data coming in.

This is what’s happening under the hood every time a web page is loaded. You will see the images for your site, scripts that you have in place, and (hopefully) that your Google Tag Manager code has fired correctly.

Developer tools network tab

In search field, enter gtm and start looking for the line with gtm.js?id=GTM-XXXXX (I replaced the actual ID with XXXXX). If its status is 200, you’re good to go! 200 means OK.

You can also search for analytics.js (that’s Google Analytics main script), collect?v= (that’s Google Analytics Hit Track), etc.Developer tools analytics

Actually, the network tab is an invaluable troubleshooting tool for any webmaster or website owner, and it goes well beyond just using GTM. You can use this tool to fully understand the footprint of your site on the web, how your images or scripts may affect load time, etc. This can be very powerful, revealing, and takes to the whole another level.


#5. Track JavaScript Errors

Here at Omnisend (P.S. we’ve just rebranded from the old name, Soundest) we constantly track JavaScript errors. They let us find most bug-infested parts of the system and eradicate those errors for good.

Our tool of choice is TrackJS. It’s a really easy-to-use platform which empowers us to see how we are doing. Errors caused by Google Tag Manager or a Custom HTML are also spotted and displayed in comprehensive reports.


TrackJS errors

This was especially useful when I was trying to implement Mixpanel. Apparently, Mixpanel does not like when their main script is fired more than once on the same page (but that’s a different topic for another blog post).

To install TrackJS, ask a developer to add their tracking code to the website (all pages) and, preferably, as the first script on the page. That’s it! From that moment the tool will start tracking everything that’s going on your website and you’ll start seeing the data really soon.


#6. GA + GTM? Check Real-time reports!

One of the most common tips I give to my students is to always check Google Analytics Real-time reports. Since the majority of you use GTM to implement various tracking stuff related to GA, real-time report is a real-time saver (pun intended).

I remember those days when we had no real-time and I had to wait for approx. 24 hours for the data to populate in GA. It was even worse if I made an implementation mistake. Then I would need to wait another 24 hours for the data to show up.

Google Analytics Real Time Report



Check if Google Tag Manager is Working: Final words

Here are my 6 tips how to check if Google Tag Manager is working properly. If I had to choose 3 most commonly used, that would be Preview and Debug Console, Tag Assistant, and GA Real-time reports (because every project I’ve worked with was using GA at some point). But, please, do not underestimate others, in fact, I’m starting to use the rest of them more and more often.

Did I miss anything? Are the any other techniques that you use to check if Google Tag Manager is working? Let me know in the comments!

Julius Fedorovicius

Head of Developer Operations at Omnisend. I am highly interested in Google Tag Manager, Google Analytics, Adwords, Email marketing, Email Deliverability, Digital Marketing in general. You can follow me on Twitter or Linkedin.