Open 0xr.space, press Open and choose the .gcode, .gco, .nc, .tap or .g. A print is drawn as the lines the nozzle lays down, at their real width and layer height, coloured by feature: outer and inner walls, infill, support, top and bottom, bridges, skirt and more, read from the comments Cura, PrusaSlicer, OrcaSlicer and Bambu Studio write. A CNC or laser job with no extrusion is drawn as its cuts, arcs included.
It shows the finished toolpath, not the print in progress: there is no layer slider and travel moves are not drawn. Very long files are simplified to within half a millimetre to fit. It does not slice, and it does not talk to a printer.
Not yet. The whole toolpath is shown; a section plane cuts it at any height.
No. Only extruding moves, or cutting moves for CNC, are drawn.
No. Binary G-code is not read; save plain .gcode from the slicer.
Yes, when the file is G-code text. A .tap that is something else, such as a ZX Spectrum tape, is refused with a message.
No. It is read on the device, and nothing is sent to a server unless you create a share link yourself.