Methods, systems, and computer storage media are provided for tracking an advertisement based on the advertisement's context. When an ad event is received on a client-computing device, a single URL is determined to display an item and track a context of the ad event. A first parameter related to the ad event is encoded as a HTTP header, and a second parameter related to tracking the ad event is encoded as a query parameter appended to the URL. The URL with the HTTP header is called, causing a domain server named in the URL to extract the first parameter from the HTTP header and the second parameter from the query parameter in order to determine the context of the ad. The domain server asynchronously requests tracking of the ad based on the context. Additionally, content for a landing page is received from the domain server.