What Is a MIDI Tester?
A MIDI tester displays the live messages sent by a connected MIDI keyboard or controller - which notes are pressed, how hard (velocity), and any control changes like mod wheel or pitch bend. It's useful for debugging a MIDI keyboard, learning the protocol, or confirming a device works before a recording session.
How to Use the MIDI Tester
- Connect your MIDI keyboard or controller via USB (or a MIDI interface).
- Grant MIDI access if your browser prompts you.
- Play a note - it appears instantly in the event log along with its velocity.
- Try the mod wheel, pitch bend, or other controls to see their values update live.
How It Works
This tool uses the Web MIDI API, requesting access via navigator.requestMIDIAccess(). Once
granted, it listens to every MIDI message from connected devices and decodes the note number, velocity, and
control data according to the standard MIDI message spec, displaying each event as it arrives.
Understanding Your Results
- Notes appear the moment you press a key - your MIDI keyboard and connection are working correctly.
- Velocity stays at a fixed value regardless of how hard you press - some budget keyboards don't support velocity sensitivity, which isn't necessarily a fault.
- No device detected - check your USB/MIDI interface connection and confirm your browser supports Web MIDI (Chrome and Edge have the best support).
- Notes appear delayed or dropped - could indicate a USB connection issue or driver problem.
Benefits
- Debug a MIDI keyboard without opening a full DAW (digital audio workstation).
- Learn how MIDI messages work by seeing raw note, velocity, and control data live.
- Confirm a used MIDI controller works fully before buying.
Common Mistakes to Avoid
- Using a browser without Web MIDI support - Safari has limited or no support; Chrome and Edge work best.
- Not granting MIDI permission - check your browser's site settings if you don't see a permission prompt.
Frequently Asked Questions
Why isn't my MIDI device showing up?
Confirm you're using a browser with Web MIDI support (Chrome or Edge work best), that you've granted MIDI permission, and that your device is properly connected and recognized by your operating system.
Does this work with USB MIDI interfaces, not just keyboards?
Yes, any device that sends standard MIDI messages through a USB or virtual MIDI connection recognized by your OS will work with this tester.
What is velocity in MIDI terms?
Velocity represents how hard or fast a key was pressed, typically on a scale of 0–127, and is used by instruments to control volume or tone dynamics.
Conclusion
This tester gives you a fast, no-software way to confirm your MIDI device is sending correct data. If you're also testing other input hardware, try the Gamepad Tester.