I need to see the request/response to a mongo server. MongoDB has an application called "mongosniff", but it isn't available on windows.
What is my alternative? Fiddler?
mongosniff isn't included with the binary download for Windows, but you can compile it yourself if you are patient and so inclined. You will need to install developer tools including Git for Windows, Scons, and the WinPcap developer's pack so this certainly isn't a quick path.
I would instead recommend downloading Wireshark which is a cross-platform network protocol analyzer. In fact, I would recommend using Wireshark in preference to mongosniff even if you aren't using Windows.
Wireshark also uses the WinPcap library and provides a much more comprehensive user interface than mongosniff as well as a huge selection of supported protocols including the Mongo Wire Protocol.
Fiddler is a web proxy for debugging HTTP/HTTPS traffic, and isn't directly relevant to the Mongo Wire Protocol. You could use Fiddler to inspect a web interface (eg. REST API), but it does not decode lower level protocols.