Google Tag Manager

Enable preview mode

To enable preview mode, click on the arrow next to the publish button and select Preview.

Use preview mode

Once the preview mode is enabled, navigate to the site where the container is implemented in the same browser tab and you will see a debug console window at the bottom of your browser showing detailed information about your tags , including their firing status and what data is being processed.

Google: Preview and debug containers

Google Tag Manager for Single Page Applications

Codeproject: Google Tag Manager

Campaign Tagging using Sitecore

Unlock the GTM Data Layer