Disclosed are various embodiments for tracking user behavior relative to a network page and identifying user interest in various content items of the network page according to the user behavior. A network page that includes multiple content items is rendered for display in a client. A user action is obtained relative to the network page. A user behavior report is sent to one or more servers. The user behavior report indicates the user action, a timestamp associated with the user action, and one or more of the content items that are associated with the user action.