1. A computer-implemented method, comprising: maintaining, by a computer system associated with an electronic marketplace, a collection of universal resource locators (URLs) and metadata, the metadata describing user characteristics associated with access to a plurality of web pages corresponding to the collection of URLs; receiving, by the computer system from a computing device of a user, a request for information about an item offered with the electronic marketplace; inserting, by the computer system in a first web page, code and a URL of the collection of URLs, the first web page associated with the electronic marketplace and comprising the information about the item, the URL corresponding to a second web page of the web pages, the code configured to, upon execution, determine whether the second web page was accessed; providing, by the computer system, the first web page to the computing device based at least in part on the request for the information; receiving, by the computer system from the computing device, an indication that the second web page was accessed prior to providing the first web page to the computing device, the indication received based at least in part on an execution of the code at the computing device; and associating, by the computer system, the user with a user characteristic from the metadata based at least in part on the indication, the user characteristic corresponding to the URL corresponding to the second web page.