MIDI Device Tester: Check Connections and Messages with Web MIDI
Plug in a MIDI keyboard or pad controller to check that the browser sees it and exactly which MIDI messages your keys, knobs and pedals send. To play notes without hardware, try the Virtual Piano. Messages are only shown on this page and never sent to a server.
🔒 Runs in your browser · Your data is never sent to a server
Press "Connect MIDI devices" and your browser will ask for permission to use MIDI.
Input ports
- No input ports found.
Output ports
- No output ports found.
Message log
No messages received yet.
How to use
- Connect your MIDI device to the computer (USB, for example) and turn it on first.
- Press "Connect MIDI devices" and allow access in the browser prompt.
- Check that your device is listed under "Input ports", then play keys, turn knobs or press pedals and watch the "Message log".
- If an output port is listed, press "Send test note" to sound the device.
Notes
- Web MIDI is mainly available in Chrome, Edge, Opera and other Chromium-based browsers. Firefox handles MIDI permission differently and may not work. Safari (including iPhone and iPad) is not supported.
- It only works on HTTPS pages, and the browser asks for permission when you connect. If you refused, allow MIDI again in the site settings.
- If another app such as a DAW has taken over the device, the browser may not see it. Close the other app and connect again.
- The log keeps the newest 200 messages, newest first. Older ones are dropped automatically.
- MIDI clock and active sensing arrive in large numbers, so they are hidden by default.
- System Exclusive (SysEx) messages are shown by type only. This page does not request SysEx permission.
Glossary
Web MIDI
The browser API for talking to MIDI devices. A page can list the connected ports and receive or send MIDI messages.
Velocity
How hard a key was struck, from 0 to 127. A Note On with velocity 0 is conventionally treated as a Note Off.
Control Change (CC)
A message for knobs, sliders and pedals. Each number has a role: CC1 is modulation, CC7 is volume and CC64 is the sustain pedal.
Pitch bend
The wheel that glides the pitch up and down. The raw value is 14-bit (0 to 16383) with 8192 meaning no bend; this page shows it centred on 0 (-8192 to 8191).
FAQ
Which browsers can test MIDI devices?
Chrome, Edge, Opera and other browsers with Web MIDI support, on desktop and Android. Firefox handles permission differently and may not work, and Safari (including iPhone and iPad) is not supported. In an unsupported browser this page tells you so.
My device is not listed after I press "Connect MIDI devices".
Check the device power and USB cable, and make sure MIDI is not blocked in the browser site settings. If another app such as a DAW has taken over the device, the browser may not see it. Close that app, reload the page and connect again.
Why does it ask for permission, and why HTTPS?
A MIDI device is external hardware, so the browser asks before a page can use it, and it only allows this on secure HTTPS pages. Messages are only displayed on screen and never sent to a server.
Why do I not see MIDI clock messages?
MIDI clock and active sensing arrive dozens of times per second and would bury the notes and CC messages you want to check, so they are hidden by default. Tick "Also show MIDI clock and other frequent messages" to see them.
A Note On with velocity 0 is shown as Note Off. Is that a bug?
No. By MIDI convention a Note On with velocity 0 means Note Off, and many keyboards release keys that way. This page shows it as Note Off to match.
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