Tag Platform

The Preview window in detail

1. In the Summary section, you can see a list of all the incoming requests intercepted by the server container and made available for Preview mode.
   Requests that start with js?id=G-XXXXXXXX are requests for the Google Tag JavaScript library.
   Requests that start with collect?v=2 are Google Analytics requests dispatched by your browser tag.
2. In the Request tab, you will see the HTTP requests coming in and out of the server and which client claimed them.
3. In the Tags tab, you can see which tags fired. In this case, the Google Analytics tag was fired in the server container.
4. The Variables tab contains information about all accessible variables sent through the request.
5. Event Data shows you the event data object constructed by the client.
6. Console shows you useful log messages.

The indented entries in the list are for event data generated by clients. In the screenshot above, the incoming collect?v=2 request generated an event data object for the event name page_view.

With the event (1 page_view) selected, you can click the tabs for Tags, Variables, and Event Data to see how the server container works with the parsed request from the browser.

With either the collect?v=2 entry or the page_view event selected, click the Request tab in the Preview mode. You should see an entry in the Outgoing HTTP Requests from Server. This means that your Google Analytics tag successfully forwarded the hit to the Google Analytics servers.

Also, with the event (1 page_view) selected, you can compare the Incoming HTTP Request value (in the Request tab) and the Event Data tab contents to see how the Google Analytics client parsed the incoming HTTP request into the event data object.

Incoming request

What the incoming HTTP request looks like:

Generated Data Object

The client-generated event data object:

With this event data object, you could add additional tags from different vendors to the server container and have them utilize this information, too.

Once you are happy with this test run, you can Publish the server container and your browser tag(s) to enable this data flow for all your site visitors.

Manual verification with Browser DevTools

In addition to Tag Manager's preview mode, you can verify that your browser is successfully sending requests to your tagging server using your browser's developer tools.

Verify with browser developer tools

To verify that your tag is sending data using your browser's developer tools:

1. Open your website in a new browser tab or window.
2. Open your browser's developer tools (usually by right-clicking and selecting Inspect, or pressing F12).
3. Navigate to the Network tab.
4. Make sure you can capture all network traffic:
   • Check the Preserve log checkbox so requests aren't lost during page reloads or navigation.
   • Reload the page if necessary to capture initial requests.
5. In the filter box, type g/collect (the common path for Google Analytics data collection) to narrow down the hits.
6. Look for requests to google-analytics.com/g/collect (for Google Analytics) or your server container URL.
7. Verify that the request was successful:
   • Status Code: Look for 204 No Content or 200 OK.
   • Payload: Click the request and check the Payload (or Query String Parameters) tab to make sure the Measurement ID (tid) and event parameters are being sent.

When looking at the requests in the Network tab, you can verify server-side specific parameters:

• Requests sent to your Server Container URL instead of google-analytics.com.
• Parameters like v=2 for Google Analytics hits.
• The cid (Client ID) matching between the browser and server logs.