Most people in the world do not have the capabilities to process the User-Agent header to figure out what type of device is calling them. User-Agent header alone sometimes does not correctly identify a calling device, such as the case of Opera Mobile/Mini web browsers which use their own User-Agent. The Blueprint platform processes these headers and detects the device being used, and forwards the detected device to the widgets via the X-Device header. Information about the actual client on the device being used (Web Browser, Y!Go, etc) is sent via the X-Client header.

Yahoo! Mobile has a catalog of (mobile) devices, called Device Catalog, which is also the piece responsible for matching the headers to a device id. This device id is the first number you see in the X-Device header, which is followed by the Make and Model of the device. The Device Catalog also provides additional device attributes such as screen and media capabilities. Currently, Device Catalog is not open to the public, only Yahoo! mobile is able query Device Catalog. We are working on plans to open Device Catalog to the world, but it will not likely happen this year. In the mean time, we have been selecting device attributes to trickle down to the widgets via an X-Device-Attributes header.

X-Device-User-Agent/X-Original-User-Agent are not related, and only provides information the original User-Agent of the device. This header is usually sent when the device is accessing a web page via content transformation/transcoding service such as those used by Yahoo!, Google and others. This is used because the User-Agent header contains the User-Agent of the content transformation/transcoding service, not the device.