Post #86: Godot's @tool
Godot provides @tool, which allows you to execute your script code in the editor!
The Godot docs have a good example of this here.
Their example is the following:
@tool
extends Sprite2D
func _process(delta):
rotation += PI * delta
This will rotate the node, and the rotation should be visible within the editor!
(Please see the docs for the info, code, gif, and more.)