Playing with a MIDI keyboard
Plug the keyboard in by USB (or pair it over Bluetooth MIDI), then press Connect MIDI keyboard under the piano and accept the browser’s request for MIDI devices. Every key you press lights the matching key on screen and plays the sampled piano. The page starts with all 88 keys, from A0 at the bottom to C8 at the top, so a full-size or 76-key controller has every one of its keys in view, and each key is named with its octave: middle C is C4 and carries a small dot.
The piano follows how hard you play. A MIDI keyboard sends a velocity from 1 to 127 with each note, and soft notes come out both quieter and darker, the way an acoustic piano responds, with two sets of recordings for soft and hard playing on a computer. Hold a sustain pedal (controller 64) and notes keep sounding after your fingers leave the keys. If your keyboard has a panic button, its All Notes Off and All Sound Off messages work too.
Fewer keys, bigger keys
88 keys make each key narrow on a laptop screen and very thin on a phone. If your keyboard has 49 or 61 keys, choose the same number under Keys so the keys on screen are larger. The octave buttons only move the computer keys; MIDI notes always play their own pitch.
Recording what you play
Hit Record, then play. Nothing is captured until the first note, and from then on each note is stored with its timing, its velocity and every pedal change. Download MIDI saves it as a standard MIDI file at 120 BPM for GarageBand, Logic, Ableton, FL Studio or MuseScore, and Download WAV renders it as audio with the same piano and room reverb you heard.
If notes go missing or one key plays much louder than its neighbours, test the keyboard itself with the MIDI tester, which shows each note and velocity as the keyboard sends it.