Tell if a site is running PHP or ASP

[dirkfirst]

How can you tell if a site is running PHP or ASP? That is, if you can not see the file extensions like .php or .asp.

[Crane]

I think you can look at the return headers somehow but I am not sure.

[Dan]

Thats correct crane - you need to look at the HTTP response headers,
if the server is PHP it will most likely say something like

X-Powered-By: PHP/4.4.2

and if it is asp it will say something like:

Server: Microsoft-IIS/5.0

[dirkfirst]

Great, thank you guys! This helps a lot!

[Kaabi]

This is helpful to know, except I can't see myself usefully applying this knowledge anytime in the near future.