Systems and methods of identifying ad elements of web pages via a computer network are provided. A script configured to identify an ad slot on a web page can be obtained by at least one data processing system having an ad slot evaluation module. The script can be executed to obtain advertisement parameters of the ad slot and web page parameters of the ad slot and generate a unique identifier of the ad slot. The generated unique identifier is associated with a URL identifier of the web page. The data processing system evaluates at least one database to determine one of a presence and an absence of the historical ad slot data. The data processing system provides content for display in the ad slot of the web page based at least in part on a result of the evaluation of the database.