I was bothered by many other solutions that are offered here, that the tools are attached quite far back. Thus, you have to awkwardly reach behind the frame. With this holder, the tools are attached further forward, so that you can grab them more easily. They are positioned in such a way that the printer is not restricted in space, i.e. the full print bed can be used. This also applies when other expansive mods are mounted on the extruder.
Furthermore, the holder can be mounted alone or in combination with suitable toolboxes above the PSU, e.g. like this https://www.prusaprinters.org/de/prints/52778-prusa-i3-mk3s-clip-on-tool-tray (also visible on pictures).
For users who prefer other hooks, I have added the STEP file for own modifications.
You can print as you like in PLA, PETG (which I prefer) or whatever, using 30% infill for better stability without any need for supports or a brim. 
Have fun printing and using it!