A gCode viewer is essential when doing anything with a CNC. Knowing where the tools is going to run can mean the different between a failed cut and a broken bit. Or let’s say you’re trying to debug some gCode scripting, no need to wait an hour to find out you messed something up. That’s where a GCode Viewer can help.
There are several on-line options that let you upload files and see them in a 3D view. However, if your CNC is setup like mine, there isn’t a good internet connection available. Camotics, formerly the unfortunately named OpenSCAM, is a cross-platform open source gCode viewer / simulator.
Most recently I used it to debug some gCode that pcb2gcode generated from a Kicad board I am working on.
Check out more about Camotics on their site: http://camotics.org