Why is Google Tag Manager preview mode not working?

One of Google Tag Manager's standout features is its Preview Mode. It allows users to test and debug tags before deploying changes to their website. If you're facing problems with GTM Preview Mode not functioning correctly, you're not alone! 

In this article, we'll delve into common causes for GTM Preview Mode failures and offer practical solutions to get it working.

Google Tag Manager Preview Mode

GTM’s Preview Mode offers several powerful features for testing and debugging tags before deploying them to a live environment. Here are some of the key things you can do with GTM Preview Mode:

• Verify that your tags are firing as expected on specific pages or events.
• Resolve any configuration issues with your tags, triggers, and variables.
• See the order in which tags are fired and diagnose any sequencing issues.
• Ensure that your tags work correctly across different browsers and devices.
• Get immediate feedback on changes made to your tags, allowing for quicker iterations and improvements.

All you have to do is to:

1. Enable the Preview Mode in GTM.
2. Visit your website, and the GTM Debug Panel should appear at the bottom of the page.
3. Verify that your tags are firing as expected, and check for any errors or issues.

In some cases you are not able to view Preview mode in Google Tag manager. Let’s discuss the reasons and solutions together.

№1. Your browser does not accept 3rd party cookies

This issue often affects a small percentage of Chrome and Safari users, where strict privacy settings block third-party cookies. And this prevents GTM Preview Mode from working correctly.

Solution.

Adjust your browser settings to allow third-party cookies. Here’s how you can do it for Chrome and Safari:

For Chrome:

1. Open Chrome and click on the three-dot menu in the upper-right corner.
2. Select "Settings" and then "Privacy and security."
3. Click on "Cookies and other site data."
4. Choose "Allow all cookies" or "Block third-party cookies in Incognito."
5. Alternatively, add an exception for GTM by clicking "Sites that can always use cookies" and entering the GTM domain.

For Safari:

1. Open Safari and go to "Preferences" from the Safari menu.
2. Click on the "Privacy" tab.
3. Uncheck the option "Prevent cross-site tracking."
4. Close the Preferences window to save the changes.

№2. Unpublished container + GTM snippet not added to website code

When you create or make changes to a container in GTM, those changes are not automatically applied to your live environment. Instead, they remain in a draft state until you explicitly publish them.

Solution.

Publish the container: click on the “Submit” button located in the upper-right corner of the GTM interface.

Check GTM snippet is added: 

• With Tag Assistant extension.
• In the website's source code. Click Ctrl + U (Mac: Cmd +Option +  U) in your browser and look for the GTM container code there.

If is is not added:

1. Log into GTM and find the container ID.
2. Add the GTM container code snippet to your website’s and sections.
3. Ensure the code is correctly placed and not commented out.

№3. Your browser is blocking pop-ups and redirects

Many modern browsers have built-in security features that block pop ups and redirects to protect users from unwanted content and potential security risks. When you click on the Preview button, a new tab should appear. GTM Preview Mode may not be able to load this essential interface.

Solution.

Adjust your browser settings to allow pop-ups and redirects for GTM. Usually, you just have to click Settings → Privacy and security → Pop-ups and redirects → Allow to send pop-ups and use redirects.

№4. Adblockers and other browser extensions can block GTM Preview Mode

Adblockers and privacy-focused extensions aim to improve user experience by blocking advertisements, trackers, and other scripts that can slow down browsing or infringe on privacy. However, these extensions may also block GTM scripts and the necessary components for Preview Mode.

Solution. 

You may need to adjust or disable your adblockers and other extensions. Here’s how to do it:

1. Whitelist GTM and Your Website or temporarily disable extensions:

• Add your website and GTM domains (e.g., www.googletagmanager.com) to the whitelist to allow them to load and execute normally.

• Go to your browser’s extensions or add-ons page, find the relevant extensions, and toggle them off.

2. Use an Incognito/Private Window:

• Open an incognito or private browsing window, where extensions are usually disabled by default (unless explicitly allowed).
• Log into GTM and activate Preview Mode from this window to see if it resolves the issue.

3. Check Browser Developer Tools:

• Use the browser’s developer tools (F12 or right-click and select “Inspect”) to see if there are any blocked requests or errors related to GTM.
• This can help identify which extension or setting is causing the problem.

4. Clear Browser Cache and Cookies:

• Clear your browser cache and cookies and then reload your website and try activating Preview Mode again.

Conclusion

Google Tag Manager's Preview Mode is a great tool, and learning how to manage it can make your life much easier. Even if you run into problems, don't worry — most issues have straightforward solutions. By understanding the common causes and knowing how to fix them, you can confidently test and debug your tags. This way, you can be sure everything works perfectly before going live. 

If you have other problems in Google Tag Manager, let us know in the comment section. We're here to help!