How to load a Tool DLL?

I have a .DLL that contain a Unity tool (or editor, whatever).

It works fine if I drop it in the Assets folder of my project, but I would like it to load with Unity, independently of the current project.

Is it possible? Does Unity has a folder that automatically load the contained DLL?

In the assets folder create a folder called “editor” and put the .DLL in there and It should work just fine.