That would be pretty useful, right? Right now it's very common to User Agent "sniff" when you want to make a server-side decision about what to give the client. But UA sniffing has always sucked and sucks more every day. What you really want to know is stuff like "how big is the screen I'm serving to?" or "does the device I'm serving to have touch events?" - that way you can serve resources that are appropriate to those questions. Is there a way to get accurate client side information on the server side?