Is there any tool that produces a diagram of the current keyboard layout, and shows secondary characters typed when pressing Shift or Alt Gr (or is editable so I can manually add those)?
An example from Wikipedia:
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Sign up to join this communityYou can use the windows built in tools "On Screen Keyboard" and the "Snipping Tool" to get an image of the current keyboard layout:
Then the one with the AltGr button pressed:
And use just about any image editing program, personally I used Gimp, to recolor and merge one on the other with a little offset for clarity: