Recently I tried to QA some tags within Google Tag Manager but had issues with the debugging console actually showing up. What was particularly perplexing about this issue was that the preview pane would show up for the non-secure version of the website, but not the secure version of the website. After doing a quick Google search and running through the 17 possible suggestions to fix the issue provided by Analytics Mania, I was still at a loss.
Luckily I work with some pretty smart developers who were able to determine it was a problem with the way the base tag was working. Once that was fixed, we were able to see the preview pane and debug our tags without a problem
What is a Base Tag?
The base tag, also called the document base URL, is a tag located in the header that “specifies a default URL and a default target for all links on a page” (W3 Schools). So say for example you have a domain called link going to your About Us page and the link is simply /about-us/. Your base URL will determine the domain attached to /about-us/. A base URL isn’t required in development. Depending on how it’s implemented, it can help you or hurt you. In our case, it hurt us.
Relativity and GTM’s Debug URL
Google Tag Manager’s main script is a secure script. The debug script is a relative script. You can tell that because instead of starting with a hostname, it starts with //.
Most times the relatively of GTM’s debugging URL isn’t an issue. However if the base URL forces an unsecure URL, the preview mode won’t work. If you see this issue, please contact your developer to update the base tag to reflect a secure URL. Voila! Your preview pane will be working again.
Summary
The list of reasons why Google Tag Manager preview pane won’t show up is seemingly endless. Reviewing your base tag can be one more check on your list to ensure you can properly debug your tags.