Isn't fiddler intended to be used to capture requests sent from already running apps and not to make standalone requests to APIs? Additionally it is not multi-platform as far as I know, you can only run it on Windows machines.
I've used Fiddler both for capturing existing requests as well as firing off my own to test an API :) You can create one from scratch or modify one that was previously captured (the latter being really handy for dealing with auth and large payloads).
Re xplat: they recently announced a cross-platform beta that will replace the Windows-only one in the long-term; I haven't tried it myself though.
