what is the easiest way to tell mach that the vfd/spindle is running or not?

I am planning on just manually turning the the spindle on and off but I am concerned with how finicky the vfd can be sometimes. What is the easiest way to tell mach that the spindle is running or not? The only thing I am concerned about is the spindle faulting out for some reason and the machine just keeps going because it does not know the spindle has stopped. I am using a hitachi wj200vfd with the ebay special 2.2kw

I'm not really interested in controlling the spindle with mach I do not really need that I just want to be safe and not end up with a machine crash scenario because of a faulted spindle.

That drive has a relay that can be programmed for many purposes, one of those being Drive Fault. Just wire the relay into your E-stop circuit and if the drive faults it will trip the E-stop.

Another couple of outputs that I used was at-zero-speed to indicate if the spindle was running, e.g. start the coolant pump etc.
The other was up-to-speed in order for the Sxxx block to carry on to the next instruction.