MIDI Tester
Test MIDI keyboards, drum pads and controllers. Live monitor for note on and off, control changes, pitch bend and velocity.
Use Chrome, Edge, or Opera. Safari and Firefox lack WebMIDI.
What the MIDI Tester does
This monitor uses the WebMIDI API to list every connected MIDI input and stream a live log of messages: note on and off, control change, pitch bend and program change, with velocity and value data. Use it to verify a new MIDI device or debug a stuck note.
How to run the test
- Connect the MIDI device over USB or a USB MIDI interface.
- Open this page. The browser will ask permission for MIDI access; click allow.
- Play notes, twist knobs, hit pads. Every message appears in the live log with device name, type, and data.
- For stuck notes, watch the log for a note on without a matching note off.
What MIDI actually sends
MIDI is a stream of small binary messages. A note on message says which key was pressed and how hard (velocity 0 to 127). A note off message says which key was released. Control change messages carry knob and slider values, again 0 to 127. Pitch bend is a 14-bit value from -8192 to 8191. This tester decodes each message type and shows the raw byte values so you can verify your device sends what you expect.
Diagnosing a stuck note
A stuck note is what happens when your DAW keeps playing a pitch after you released the key. In MIDI terms it means a note on was sent but the matching note off never arrived. Play the offending key with this tester open and watch the log. If you see a note on but no note off, your keyboard has a hardware fault (usually a worn key contact). If you see both messages, the problem is in the DAW, not the keyboard.
Velocity curves and how to read them
Velocity is how hard you pressed a key. Different keyboards have different sensitivity curves: some make it easy to hit 127 (loud) and others compress everything into 60 to 100. Play a scale gently and read the velocity numbers. If your soft touches are already at 90, the curve is too aggressive and you should soften it in your keyboard's settings menu. If your hardest hits max at 80, the curve is too gentle.
Control changes, knobs, and modulation
Every knob, fader, and expression pedal sends a control change (CC) message with a controller number (1 to 127) and a value (0 to 127). CC 1 is the mod wheel by convention. CC 7 is main volume. CC 11 is expression. This tester shows which CC number your knob is sending, which is exactly what you need to know when mapping it in a DAW. Twist the knob and see the number scroll.
Why WebMIDI does not see hot-plugged devices
The WebMIDI spec makes the browser enumerate MIDI devices at page load time. If you plug a device in after loading, it will not appear until you refresh. This is a security decision, not a bug. If your device is missing, unplug it, reload the page, then plug it back in and it will appear immediately.
Common problems and quick fixes
Common questions
Why is my device not listed?+
Safari or Firefox?+
Can I test MIDI output?+
Play a scale, hit each pad, twist each knob. If the log stays quiet on any control, you have found what needs fixing.
Every diagnostic here runs locally in your browser. Nothing is uploaded.
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