We take your uploaded .gcode file that was made by your slicer, and parse it line by line, with algorithms to determine where the layers start and end.
It then rewrites the file with all the extra bits you selected into it. We then give you a download link and display what we have added(Nothing is Deleted).
Once you have downloaded your new file, you can load it on to your machine to start printing.
I use this on alot of my prints, it has become the 'Norm'. Unfortunately i only use a few Slicers so it is not compatible with all of them.