1. A computer-implemented method comprising: receiving from a consumer application via a data network interface a request for activation of a keyword extraction service via an application programming interface, the request for processing by a processor of a computer system, the request including an identity of a content source, the request further including an identification of a particular extraction process of a plurality of selectable extraction processes, the particular extraction process as identified in the request is selected for use by the keyword extraction service on the identified content source, the keyword extraction service to extract un-registered keywords from the identified content source using the particular extraction process as identified in the request and to rank the extracted keywords according to performance measures obtained from tracking aggregate user behavior on a site, the extracted keywords not having been previously registered by the consumer application, the request further including a fetch interval indicating an amount of time after which the particular extraction process is repeatedly used by the keyword extraction service on the identified content source; determining whether the keyword extraction service has already processed the identified content source and retained extracted keywords in a data store; extracting keywords from the identified content source using the particular extraction process identified in the request; and making the extracted keywords accessible to the consumer application.