April 5, 2025
How to check if Google Tag Manager is Working?
Updated: September 5th, 2025
Google Tag Manager. The thing that makes the lives of marketers and web analysts easier. However, the purpose of this blog post is not to convince you to start using it (I have another one that explains all GTM benefits). Today, I assume 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 to each other. If possible, you should use all or at least half of them.
Table of Contents
– Here’s what you will learn in this article –
- Video tutorial
- #1. Check the website’s source code
- #2. Enable the Preview and Debug mode
- #3. Leverage Screaming Frog
- #4. Chrome’s developer tools
- #5. Google Analytics 4 + GTM? Check the DebugView
- Caching
- Final words
To check if Google Tag Manager is working, you need to complete the following steps:
- Check the website’s source code (and use the “Search” feature)
- Enable the Preview and Debug mode. Did it appear? Is everything working?
- Leverage Screaming Frog
- Check Chrome’s developer tools
- Check Google Analytics real-time reports or DebugView (if you have configured any events or pageviews)
Now, let’s take a closer look at every step individually.
Video tutorial
If you prefer video content, some of the tips are explained in the video below. But if you want to know ALL the possible options, then read the blog post as well.
#1. Check the website’s source code
- Visit your homepage (or any page on your website)
- Right-click with your mouse (anywhere on the page background) or key and click “View Page Source” (or just hit CTRL + U on your keyboard)
- When viewing your page source, do a Control + F, which will bring up your “find” function within your browser
- Input “gtm.js” here, and if you have any matching characters, proceed to verify each instance
- If the code Google Tag Manager is present (it is surrounded by < script >), that means Google Tag Manager is working.
- Quite often, the 2nd code is implemented as well (that is surrounded by < noscript >). This code is optional but if you intend to use it, make sure that it is placed immediately after the <body> tag in the HTML. You can learn more about the GTM noscript here.
Important: make sure that all the symbols and characters in Google Tag Manager container code snippets are correct and that there are no modifications (especially by accident). For example, it’s quite popular among inexperienced marketers to share tracking codes via a Word file or Google Docs. That is a very bad practice because these platforms usually break the code by automatically changing the quotation marks. To learn more, read tip #16 here.
#2. Enable the Preview and Debug mode
The next technique to check if Google Tag Manager is working is to enable Preview and Debug (P&D) mode. To do so, click the Preview button in the top right corner of your GTM interface (near the Submit button).
This is by far the most important and reliable method on this list. While other techniques can confirm that the GTM script is present on the page, Preview Mode is the only one that shows you what is happening inside your container in real-time. It is your direct window into the inner workings of GTM, showing you which tags are firing, what data is available, and why your triggers did (or did not) work.
After you enable P&D mode, the preview mode will be opened in a new tab. It will ask you to enter the URL of the website. When you do that, another tab/window will open with your website. In the Preview mode, you should see the word Connected.
Also, at the bottom of the website’s window, you should see this (or something similar):
As long as you continue navigating your site and see some events in Preview and Debug console at the bottom of your screen, that’s a good sign.
I’ve published a detailed guide that explains what the Preview and Debug mode is and how you can make use of it.
If, on the other hand, the GTM preview mode is not working, here’s the guide on how to fix it.
#3. Leverage Screaming Frog
Another way how Google Tag Manager implementation might be broken is when the GTM container code is not added to all pages of a website. There are many reasons why things like this happen:
- The Content Management System is terrible and buggy.
- The website uses a lot of different page templates, and there is no easy way to update them all at once.
- 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 that 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 https://www.googletagmanager.com/gtm.js in the website’s source code. This URL is used by the Google Tag Manager container.
In Screaming Frog’s application, go to Configuration > Custom > Search and enter the following condition:
Does not contain https://www.googletagmanager.com/gtm.js
Enter the URL of the website you wish to check and hit the Start button.
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 to add the tracking code to those pages or ask a developer to do that.
Finding pages where the GTM code is missing is critical for data consistency. If a visitor navigates from a tracked page to an untracked one, their user journey will appear to abruptly end. This can break your session data and make it look like users are leaving your site when they are actually just moving to a different section. Using a tool like Screaming Frog to perform a complete site audit helps you find these gaps and maintain a complete and accurate picture of user behavior.
#4. Chrome’s developer tools
Another way to check if Google Tag Manager is working is to dive deeper into the developer 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.
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.
First of all, click Console and start navigating the website and keep looking for errors. If none occurs, 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 Google. Maybe others face similar issues and have come up with a solution.
By the way, if you spot this error…
404 not found for GET: GET http://www.googletagmanager.com/gtm.js?id=GTM-XXXXX
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 happens under the hood every time a web page is loaded. You will see the images for your site, the scripts that you have in place, and (hopefully) that your Google Tag Manager code has been fired correctly.
In the 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.
If you see multiple gtm.js requests, it might be caused by the GTM Preview mode. Read more.
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 and eye-opening.
#5. Google Analytics 4 + GTM? Check the DebugView
If you have implemented Google Analytics 4 with Google Tag Manager, you can check if your data is being sent to GA4. First, enable the Preview mode in GTM, then go to GA4 > DebugView and check if you see some data.
You can learn more about DebugView here.
Caching
Another important thing to mention is caching. Websites and browsers store temporary copies of files (like pages and JavaScript) to help sites load faster on subsequent visits. As a result, after the GTM container is added to the website, you might still be viewing an old, cached version of your site, making it seem like your updates aren’t live or that GTM isn’t working correctly.
First, try to do a hard refresh. Press Ctrl+Shift+R (Windows/Linux) or Cmd+Shift+R (Mac). If Google Tag Manager started working after this, then you’re dealing with cache. Remember that your website visitors (most likely) won’t do hard refreshes, so it’s a good practice to ask the developer to clear the website’s cache (otherwise, GTM won’t work for some visitors).
If you find that caching was indeed the problem, it is a good idea to communicate this with your developer. You can ask them if it is possible to temporarily disable server-side caching for your specific IP address during future GTM testing sessions. This is a common practice that allows you to see your changes instantly without having to constantly clear the cache or disrupt the speedy experience for your actual website visitors. It is a small setup change that can save you a lot of time and frustration.
This can be done in different ways (depending on your website’s configuration). Caching can be done on the website’s server level or on the Content Delivery Network (CDN) level. For example, if you are using Cloudflare as a CDN, here’s how to clear the cache.
Frequently asked questions about whether GTM is working
If you just skimmed the article, here is a list of the most common questions asked about this topic.
How do I check if Google Tag Manager is working? There are various techniques to achieve this, for example, checking the source code of the website, checking if GTM preview mode is working, checking the browser’s developer tools and outgoing requests, etc.
What is the best way to check if Google Tag Manager is working? Checking if Google Tag Manager preview mode works is definitely a good option. In combination, you could also check if outgoing requests have the 200 status.
What tools should I use to check if GTM is working? You can start with the built-in Google Tag Manager preview mode. Also, browsers have built-in developer tools.
Check if Google Tag Manager is working: final words
Here are my six tips on how to check if Google Tag Manager is working properly. If I had to choose the 2 most commonly used, they would be Preview and Debug Console and DebugView (in GA4). 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 there other techniques you use to check if Google Tag Manager works? Let me know in the comments!
17 COMMENTS
Hi Julius,
I'm using Google Tag Assistant and I keep getting the "Non-standard implementation" error for every single Google Web Property ID on every single website we own. Google won't tell you how to fix this and I can't find any documentation anywhere that does. How can this error be fixed if no one can tell you how to do it or has any documentation about it?
Non-standard implementation is not an error. GA implemented via GTM is always considered as non-standard by tag assistant (for some reason). Don't worry about it and ignore.
Great article! Thank you!!
Hi Julius
I have implemented the google tag manager successfully on my website and also checked by preview which is available on google tag manager but the problem is whenever i open my site in other browser to check real time user then it shown nothing this never happened before. Could you please resolve this issue and tell me the reason behind this. As you mentioned above i have checked all the things and everything is perfect. Then why this is happening.
Preview mode works ONLY on the same browser where you have enabled it. Even Incognito mode is excluded. If you want to see your interactions in real-time on any computer you need to:
- Either publish all changes
- Or share the preview mode (there is a link in the orange preview box)
I've tried the following in Chrome:
- enabled pop ups
- disabled extensions
- Installed Google Tag assistant (shows Global Site Tag and Google Analytics)
- allowed 3rd party cookies
- refreshed, hard refreshed, restarted browser, rebooted PC many times
- disabled Ad Blocker (one of the extensions)
- unaware of any CDN or CSP in play, this is home internet
- followed the instructions on checking configuration flags in Chrome
- no private mode, same browser instance different tabs, etc
...all from your other article.
I've also tried Brave and Safari, but had little luck even disabling blockers and such there.
Then I used Chrome Developer tools above and did not find any hits for gtm.js or my tag ##### when I was clicking around my site.
I disconnected and reconnected the GTM code inside Wix, and then after that (and only after that) noticed in Google Tag Assistant there were 4 entries for gtag.js (prior there had always been only one). There was also a warning on Google Tag Assistant about this.
Does this mean Wix is being a POS implementer, and is their poor implementation is the likely cause, or any other thoughts?
The problem is that your tag assistant does not show the Google Tag Manager. That is your problem. No GTM = no preview mode. Wix's built-in GTM integration is weird. Read this guide https://www.analyticsmania.com/post/how-to-track-wix-website-with-google-tag-manager/
Hi Julis,
I added my testing domain to tag manager and the preview mode is not showing the debug pop up.
Any reasons for it?
Yes, multiple reasons. The blog post that you are currently reading mentioned this link https://www.analyticsmania.com/post/google-tag-manager-preview-mode-not-working/
We have a tag manager account that's running for years with lots of tags that are probably not relevant anymore. How can I find out which one's are still active and which ones are not active anymore and can be removed?
It is too much work to go through it tag by tag and check ik in debug mode.
There is no simple way. You could build a tag monitoring tool, collect data for a while and then see which tags are not firing/used anymore https://www.simoahava.com/analytics/google-tag-manager-monitor/
But that is technical, complex, and time-consuming as well. You would be better off by doing a container audit (or hiring someone to do so)
Hi Julius,
I checked the status code under the "Network" tab for my GTM and it shows "307".
Does this mean the GTM is not working properly? If so, how can this be fixed?
Thanks.
Hi, please share the URL to your website
Hi Julius,
I installed GTM on a Prestashop 1.6.11 webshop that running on templates. I placed the scripted code into the header.tpl-s part. It works well in practice, but when I look to the source code the scripted code is moved way down to the bottom of the part. The noscript code stayed in it's original place. Tag Assistant also is blue instead of green and says "GTM JavaScript code not found as a direct child of the tag".
I know it's not an error, but I can't really figure out the reason for it, and not sure if I should just ignore it. Also I found that others had the same problem, but couldn't find anyone mentioning a solution.
(Uh, it seems like "head" and then later "body" was removed in front of the words "part" because I used angled brackets.)
Do you have any articles about GA4 and detecting AdBlock sessions with GTM?
Hello,
I have a super weird issue. I am using both UA and migrating to GA4, both installed via GTM.
In STAGING ENV property - both UA and GA4 work fine.
In PROD ENV property - UA works fine, while GA4 doesn't.
All checks I have done for PROD:
-In network tab, there are collect calls for UA, but not for GA4 EXCEPT at login page. No collect calls after that page.
-Weirdly, preview mode shows me the page views/navigation from PROD
-Google Tag Assistant shows me all 3 tags in both PROD and STAGING.
-Real time reports and debug mode in STAGING work fine, in PROD only the log in page shows, and after that nothing.
-I don't have an ad blocker in my chrome browser
What is even weirder, I have GA4 installed in PROD for some time, and it does show me user visits, just half the ones from UA.
Could you please give me any ideas how could I solve this problem? Does anything come to mind?
Thank you