The MobileESP project seeks to provide web site developers an easy-to-use and lightweight API for detecting whether visitors are using a mobile device, and if so, what kind. The APIs provide simple boolean results (“true” or “false”) for identifying individual device categories (such as iPhone, BlackBerry, Android, and Windows Mobile), device capabilities (e.g., J2ME), and broad classes of devices, such as “iPhone Tier” (iPhone/Android/WebOS) and smartphones.