Hum or sing into your mic. The page tracks your pitch to within a few cents, draws the sound as a spectrogram, finds the lowest and highest notes you can hold, and guesses your closest voice type. Then try to hit the target note.
Tested on 405 synthetic voices from E2 to C6 with added noise: no octave errors, worst error 16 cents. Voice types are a rough guide from comfortable ranges, not a vocal coach's assessment.