I am planning on making several new magic items and spells, as well as allowing my players to make some.
As far as I know, the rules in the DMG only describe the relevant spell levels for spells that involve damage, in its table. For magic items that don’t act like spells, for example: a ladder that can expand or compress down, I haven't found any way to assign them a rarity.
How do I determine the rarity or spell level for unique effects that don't do damage? I will allow content outside of the main books to be used in the answer.