What are you generating the toolpath with?
If you are importing from autocad, fusion, or inventor, you can generate the toolpath gcode in the same application and see preview there, as well. Then, load the .nc file and cut.
It is easiest in Fusion, as it includes the CAM unit as a core piece. For Inventor, you need HSM. 2.5D is free. I have not used Autocad for CAM applications, but have moved Autocad models int fusion and Inventor (these days, I primarily use Inventor due to the day job, so I am out of date on Autocad other than for 2D applications, usually client files)
If you are importing someone else’s files and don’t have the CAD packages, Fusion is free for most non-commercial use (see their website), as is a lite version of Inventor.