Find your level in Japanese
A free test of up to 20 questions, a few minutes long, with no account needed. At the end it suggests the level to start at.
It starts easy, four questions a level, and stops as soon as the questions get hard for you, so most people answer fewer.
If you don't know an answer, say so rather than guess: the suggestion is better for it.
Never studied Japanese? There's no need for a test: start at A1. Or begin with Start here.