With the Ads Diagnostic Tool, its fundamental purpose is almost self-explanatory; to diagnose any problems that may have occurred within your campaign regarding keywords.
Therefore, the ads diagnostic tool tells you whether your adverts are showing or not showing, and also explains why in great detail.
Though limited to a campaign at a time rather than a whole account, this tool can be rather specific, by enabling you to choose specific keywords that you want to run the test for.
In order to operate, open the Adwords account, then use the ‘tools’ link within the ‘opportunities tab’, or click the icon next to the status of the keyword. (To help navigation, this icon, when clicked, usually expresses the quality score and whether the ad is running correctly).
In summary, the ads diagnostic tool, as well as being simple to implement and readily available, is critical to maintaining an account, cleaning it up and ensuring that any mistakes previously made are rectified.