Google Publisher Console is the greatest tool in the history of Ad Ops.
For complete documentation, check over here.
To bring up the console, simply append ?googfc to the end of any URL.
Let’s say your webpage is http://www.example.com/my-cool-page
Just type this: http://www.example.com/my-cool-page?googfc
Seriously, try it on your own site right now. It’s awesome.
If you Custom Criteria are not working as expected, this tool lets you see exactly what targeting information is getting sent to DFP.
Debug Actual Delivery
By clicking on the “Delivery Diagnostics” link, you can see exactly how DFP decided which Line Item to show. This is massively useful when you’ve got a bunch of line items running at different priority levels.
It works everywhere
Well, it works everywhere with DFP. So you can see how other people have setup their own websites! Of course, you can’t look inside their DFP without permission, but you can see how they’ve tagged their pages and what kind of targeting information they are passing to DFP.