How to test a MIDI device
- Plug it in by USB, or through a MIDI interface for 5-pin DIN gear, and switch it on.
- Press Connect MIDI devices and allow access when your browser asks. Your device appears under Inputs.
- Play. Keys light up on the keyboard above, with the note, velocity and chord. Knobs, faders and pedals show up under Controllers, and every raw message lands in the log.
To check that a device receives MIDI, pick it under Test an output and send a note. If it makes a sound, the connection works both ways.
What the tester shows
- Notes and chords: note name, MIDI number and frequency, plus the chord or interval you're holding. On channel 10 it also shows the General MIDI drum name.
- Velocity: how hard each key was hit, with a chart of recent notes so you can see the range your keyboard covers.
- Controllers: pitch bend, mod wheel, sustain pedal, aftertouch, program changes and every other CC with its standard name.
- Clock: tempo from MIDI clock, start, stop and song position.
- Raw messages: every message with channel, decoded data and hex bytes, ready to copy into a bug report.
Questions
Why is my MIDI keyboard not detected?
Check that it is connected and switched on before you press Connect, then press it again. Close other apps that might hold the port exclusively (on Windows, a DAW often does). Try a different USB cable or port: many cheap cables only carry power. Keyboards with a "USB to host" port need that port, not a USB stick port.
Does this work in Safari or on iPhone and iPad?
Not yet. Safari has no Web MIDI, and every browser on iPhone and iPad uses Safari underneath. Use Chrome, Edge, Firefox or Opera on a computer, or Chrome on Android. You can still try the page with your computer keyboard.
Why does middle C show as C3 on my keyboard?
There are two conventions for octave numbers. Note 60 is C4 in scientific pitch notation and C3 for Yamaha and many DAWs. Switch the Middle C setting under the keyboard to match your gear.
My keys show the wrong velocity, or always 127. Why?
Some keyboards and pads have a fixed-velocity mode or a velocity curve setting. Play from very soft to very hard and watch the velocity chart. If it never goes below a certain value, look for "velocity curve" or "touch response" in your keyboard's settings.
What is MIDI clock and why is it hidden?
MIDI clock sends 24 ticks per quarter note so other gear can follow the tempo. That is a lot of messages, so the log hides them by default. The Clock panel still counts them and shows the tempo.
Is anything I play sent anywhere?
No. Everything runs in your browser. MIDI data never leaves your computer.