Abstract: Active script can be provided with content to be displayed on a computing device to determine whether advertising, intended to be displayed with the content, is actually displayed by the computing device. The script can examine various aspects of the code used to render the content, to determine whether ad-blocking software is blocking the ad or something is otherwise preventing the advertising from being displayed. Information about the visibility of the advertising can be sent to a location such as a logging service, which can store the data until such time as the data is to be retrieved and processed, such as to determine an extent to which client devices are blocking ads to be displayed with content.