You just bought one of those small form factor keyboards thinking you are going to be hot shit, using a ton of layers to get to all numbers, symbols, macros etc.
Well, the first time using one can be really tricky. "Now where did I actually put left bracket?" you are thinking while your product manager is screaming at you to fix that bug you should have fixed 3 hours ago.
You could of course print out a paper with all your layer layouts, but that means interacting with a modern printer which is aneurysm inducing, and you long ago abandoned having one at home.
This is a simple little application for macOS that can show you an overlay of a layer on your keyboard.
You give it your QMK json layout, and it allows you to set a hotkey for a layer. Tapping down that hotkey will display an overlay (that does not steal focus) of the current layer. Tap it again to hide!