Ok. Got it.

Thanks.

Fiddler will always show whatever traffic is flowing through it (if any) unless you have filters set to hide traffic.

Properly-written client apps *should not* send traffic through Fiddler when it's not attached (which means that it isn't registered as the system proxy). Some client applications are not properly written and may continue to send traffic through a proxy that detached until they are restarted.

Hm. My mistake. I thought the traffic was going through Fiddler in any case while it's running.

So can I leave Fiddler running all the time, just enable it if necessary?

Can you please elaborate on what exactly you're trying to do and what exactly isn't working?

You can toggle Fiddler as the system proxy by simply clicking the command on the File menu or by tapping the "Capturing" icon at the bottom-left corner of Fiddler's main window.