Abstract: There are methods and apparatus, including computer program products, for receiving web-based resource requests at a first computing system from a second computing system, the first computing system and a second computing system being in electronic communication through a network, each web-based resource request being defined by one or more variable-value pairs; extracting data from the web-based resource requests, the extracted data including a set of variable/value pairs that is associated with a first subset of the web-based resource requests, the set of variable/value pairs including values that have been assigned to a uniform resource locator (URL) variable; and examining the extracted data to infer a web user agent type that is a source of the first subset of the web-based resource requests