How-to · Updated October 11, 2026
Fix Tag Manager preview mode not connecting
Updated October 11, 2026
15 minutes
Enter the final address of a page that loads this exact GTM- container, then clear what blocks the connection: ad blockers, an unanswered cookie banner, redirects. If the page breaks or keeps reloading, edit the domain in Tag Assistant and untick Include debug signal in the URL. Add the Tag Assistant extension for tags inside iframes.
Before you start
- Access to the container in Tag Manager, to start Preview from its workspace.
- The container ID, shown on the Workspace tab and starting with GTM-.
- Chrome, so you can add the Tag Assistant extension if the connection still fails.
Point preview at a page that runs this container
Preview shows your container only on a page that already loads it, so start by proving that.
- Open the page in a normal browser window and note the address it ends on. If it redirects, for example to www, to https or to a login page, use that final address; Google says multiple redirects can stop the debug window loading.
- Check that this page loads the container. Search the page source for your GTM- ID. The Tag Assistant extension's side panel also lists the tags firing on the page.
- If a different GTM- ID shows, or none, preview will not show this container on that page. Open the container the site does load, or try a page where yours is installed.
- In Tag Manager, on the Workspace tab, click Preview, enter the final address and click Connect.
Clear what blocks the connection
Any of these can stop the debug window from joining the page, so check them one at a time.
- Turn off ad blockers and privacy extensions for the site, then reconnect.
- Answer the cookie banner in the window that opens. If it still will not connect, Google says consent tools may block Google tags and should be configured to allow interaction with Google's consent API.
- If you use the Tag Assistant extension, check it has permission to read and change site data on this site.
- If the site's tag loads late, click Retry. Google says the tag can load after the point when Tag Assistant tries to connect.
- If the tags sit inside an iframe, such as an embedded booking or form tool, install the Tag Assistant extension. Google says iframe tags can be debugged only with it. Tag Assistant does not currently support AMP pages.
Drop the debug signal if the page breaks
Tag Assistant adds a debug parameter to the address, which can break some sites, and Google offers a switch to leave it off.
- If the site shows an error, reloads endlessly or otherwise misbehaves, go back to Tag Assistant and edit the domain you entered.
- Untick Include debug signal in the URL and click Connect again.
Google says that parameter helps other debugging tools, such as DebugView in GA4, show your session. With it off, DebugView may stay empty, so judge the test in the Tag Assistant window.
Check it worked
The site's window should show Connected in the bottom right corner. Go back to the Tag Assistant tab and click Continue to open the debug interface.
Click through the site: the debug interface should list which tags fired on each page and action, updating as you go. It shows only in your browser and to anyone you share the preview with, never to regular visitors.
Preview works but the live site does not
Preview runs the workspace draft as if it were deployed, in your browser only. A tag that fires there is not live until a version is created and published to the Live environment.
Let someone else preview it
Preview shows only in the browser that started it. To let a colleague see the same draft, click More Actions in Tag Assistant, then Share, enter the site's domain and send them the preview URL it gives.