MIDI Test
Plug in any MIDI keyboard or controller and watch live note, velocity and control change data right here, no DAW or software install needed.
Play your MIDI controller or the keyboard below to see live messages.
- No MIDI input devices detected.
- No MIDI output devices detected.
Play with your mouse, touch, computer keys (A–L row, W/E/T/Y/U for sharps), or a connected MIDI controller. Z / X shift octave, C / V change velocity, Tab toggles sustain.
No MIDI messages yet. Press a key above or play your controller.
Quick guide: how to use the MIDI I/O Test
Takes under a minute- 1Connect your MIDI keyboard or controller over USB or Bluetooth.
- 2Allow MIDI access when the browser asks.
- 3Select your input device, then play a note and watch the monitor.
- 4Use the on-screen keyboard and synth to test output devices.
Overview
If you've ever plugged in a MIDI keyboard, drum pad, or control surface and wondered whether it's actually talking to your computer before opening a full digital audio workstation, this tool answers that question in seconds. It uses the Web MIDI API, a browser feature that gives web pages direct, low-latency access to MIDI input and output ports, the same protocol musicians have relied on since the 1980s to connect keyboards, synthesizers, and controllers.
Once you grant permission, the page lists every MIDI input your operating system currently sees, and lets you pick one to monitor. From there, every note press, release, control knob turn, pedal press, and pitch bend movement shows up on screen in real time, decoded into human-readable values instead of raw hexadecimal bytes.
This is especially useful for troubleshooting a "new" controller before you've set up any software mapping for it, confirming a secondhand keyboard actually works before you commit to buying it, or diagnosing a specific key, pad, or knob that seems unresponsive.
How to read your results
Device list
Every MIDI input port currently visible to your operating system appears here, whether it's connected by USB, a 5-pin DIN MIDI cable through an interface, or Bluetooth. If your device doesn't appear at all, the problem is happening before the browser even gets involved, most likely a cable, driver, or OS-level pairing issue.
Note events
Pressing a key sends a "note on" message with a note number (0-127) and a velocity (0-127, how hard you pressed). Releasing sends "note off". If you see note-on events but the note numbers seem shifted by an octave from what you expect, check your keyboard's octave/transpose setting, many keyboards ship with this set to something other than zero.
Control change (CC) messages
Every knob, slider, mod wheel, and sustain pedal on your controller typically sends CC messages, each tagged with a CC number (identifying which control moved) and a value from 0 to 127. Turning a knob should produce a smooth, rapidly updating stream of values; a knob that jumps erratically or doesn't reach 0 or 127 at its extremes may have a worn potentiometer.
Channel and raw data
MIDI supports 16 channels per port, and multi-timbral keyboards or controllers with multiple zones often send different notes on different channels. If your software expects channel 1 but your keyboard is set to channel 2, notes will register here but won't trigger sounds in your DAW until the channels match.
Troubleshooting
If your MIDI device isn't showing up or isn't responding correctly, try these steps in order:
- Use Chrome, Edge, or another Chromium-based browser. Safari does not support Web MIDI, and Firefox support is inconsistent.
- Grant the MIDI permission prompt when the browser asks. If you dismissed it earlier, reset site permissions and reload.
- Check the physical connection: reseat the USB cable, try a different USB port, or confirm a 5-pin DIN interface has power if it needs its own supply.
- Confirm the device is recognized by your operating system first, using Windows' MIDI devices panel or macOS's Audio MIDI Setup utility, before assuming the browser is at fault.
- If using Bluetooth MIDI, pair the device in your OS Bluetooth settings first; the browser can't initiate pairing.
- Restart the browser after connecting a device for the first time, since some browsers only enumerate MIDI ports once at MIDI access request time.
Diagnosing specific hardware quirks
A stuck or dead key usually shows no note-on event at all when pressed, which points to a mechanical or contact issue inside the keyboard rather than a software problem. A key that fires repeatedly or "chatters" when pressed once often indicates a failing switch contact. Velocity that never changes regardless of how hard you play means the keyboard is likely set to fixed velocity mode in its internal menu rather than a hardware fault.
For control surfaces with motorized or endless-rotation knobs, watch for CC values that jump by large increments instead of smoothly incrementing; this can indicate a mismatched resolution setting between the controller and expected 7-bit MIDI range, or genuine mechanical wear.
Why the browser asks for permission
Full MIDI access, particularly with system exclusive (SysEx) messages enabled, can be used to reflash firmware or reconfigure certain hardware, so Chromium browsers gate it behind an explicit permission prompt similar to camera or microphone access. This tool only needs standard MIDI input to display notes and CCs, and nothing you do here is transmitted anywhere else; all the data stays local to your browser tab.
Frequently asked questions
Why doesn't my MIDI keyboard show up in the device list?
Most commonly the browser doesn't support Web MIDI, the USB or 5-pin DIN cable isn't fully seated, or the OS hasn't installed a driver for the interface. Try unplugging and replugging the USB cable, confirm the device shows up in your OS's own MIDI/sound settings, and reload the page after it's connected.
Which browsers support Web MIDI?
Chrome, Edge, Opera and other Chromium-based browsers support Web MIDI natively. Firefox added support behind a flag in some versions but it isn't reliably enabled by default. Safari does not support the Web MIDI API at all as of this writing, so Mac users testing in Safari will need to switch to Chrome.
The page asks for MIDI permission, is that normal?
Yes. Chromium browsers treat MIDI access, especially with SysEx enabled, as a permission-gated feature similar to camera or microphone access, because a compromised page with full MIDI access could reprogram some hardware. Click Allow when prompted.
I pressed a key but nothing shows up on screen. Why?
Check that the correct MIDI input is selected in the device dropdown if your interface exposes more than one port. Also confirm the keyboard's MIDI output channel matches what you expect, and that local control or MIDI thru settings on the keyboard itself aren't rerouting the signal elsewhere.
What do the note numbers mean?
MIDI notes are numbered 0 to 127, where 60 is commonly middle C (though some manufacturers label it C3 and others C4, an old and persistent numbering disagreement). The tool typically shows both the raw number and the note name so you don't have to memorize the mapping.
What is velocity and why does it matter?
Velocity is a 0-127 value representing how hard or fast a key was struck, which most synthesizers and DAWs use to control volume or timbre. If your velocity readings feel oddly capped or don't vary with how hard you play, check your keyboard's velocity curve setting, some keyboards let you fix it at a constant value.
What are CC (control change) messages?
CC messages carry continuous controller data like mod wheel position, sustain pedal state, volume knobs, and expression pedals, each identified by a CC number from 0 to 127. Watching these live is the fastest way to confirm a knob, fader or pedal is actually transmitting before you spend time mapping it in a DAW.
My sustain pedal doesn't register as on/off. What's wrong?
Sustain pedals send CC 64, where values 0-63 usually mean off and 64-127 mean on, but some cheaper pedals or polarity-reversed pedals send this backwards. If pressing shows 0 and releasing shows 127, your pedal or keyboard has an inverted polarity setting you can usually flip in the keyboard's menu.
Can I test a MIDI controller without any music software installed?
Yes, that's exactly what this tool is for. It talks directly to your MIDI device through the browser's Web MIDI API, so you can confirm a keyboard, pad controller, or breath controller is working correctly before ever opening a DAW.
Does this work with wireless or Bluetooth MIDI devices?
Bluetooth MIDI devices generally work once they're paired at the OS level, since to the browser they still appear as a standard MIDI input port. Pairing itself has to happen in your operating system's Bluetooth settings first, the browser can't initiate that pairing on its own.
Why do I see multiple entries for the same keyboard?
Some MIDI interfaces expose separate ports for different purposes, such as a dedicated port for standard notes/CCs and another for SysEx or a DAW control surface protocol. Seeing two or more entries for one physical device is normal and not a malfunction.