Test polyphonic key input before a music lesson

A keyboard may play every note on its own, yet miss notes when a student holds a chord. Check the MIDI input before class so you can find out whether the keyboard sends each note, or whether the problem starts later in the music software.

The MIDI Test shows incoming key activity and MIDI messages in your browser. It checks the keyboard's input, not the number of notes a particular instrument or music app can sound at once. Use Chrome or Edge on a computer, since MIDI Test does not work in Safari.

Test several held keys

1. Open the MIDI Test in Chrome or Edge on the computer you will use for the lesson. Connect the MIDI keyboard by USB or Bluetooth and allow the browser to access it if asked.
2. Press and release a few keys one at a time. Check that each press appears as key activity or a MIDI message, and that the activity changes when you release the key.
3. Hold a simple three-note chord. If all three notes register, try a wider chord or add notes one by one. Keep each test comfortable, and release the keys before trying the next combination.
4. Repeat a combination that seemed to miss a note. Try pressing the notes in a different order, then test the same keys individually again.

Testing one note at a time first is important. If an individual key never registers, that is a different problem from a keyboard that drops notes only when several keys are held. For a classroom check, test the chords or key combinations students will actually use, rather than pressing every key at once.

What the result means

Every note appears, including in chords

The browser is receiving the keyboard's note input for the combinations you tried. That is a good sign for lesson readiness, but it does not prove that every music app or virtual instrument will play the same number of notes. Test the intended app too if students need to hear the notes, not just send them.

A key works alone but disappears in a chord

The keyboard or its connection may be limiting simultaneous input. Some keyboards have a limit on how many keys they can scan at once, and a weak wireless connection or unreliable USB connection can also lose events. Repeat the chord after reconnecting, then compare with a different combination.

A key does not appear even when pressed alone

Check that the browser is receiving input from the correct MIDI keyboard. If the same key still produces no activity after reconnecting and testing another browser, the key, keyboard, or connection may be at fault.

All notes register, but the instrument stops sounding

The keyboard is sending the input. Look at the music app or instrument instead. Its voice limit, track settings, MIDI channel, or sound settings may prevent every received note from being heard. A browser test cannot measure an instrument's audio polyphony, which is the number of notes it can produce at the same time.

A note seems to stay on after you release it

The browser may not have received a note release message, often called Note Off. Test again after reconnecting the keyboard. If the same key remains active repeatedly, check for a stuck key or a connection that is dropping messages.

How to fix missed notes

1. Reconnect the keyboard. Unplug and reconnect a USB keyboard, then repeat the same chord. If you use Bluetooth, check that it is connected to this computer and not another nearby device. On Windows 11, check Settings › Bluetooth & devices › Devices. On a Mac, check System Settings › Bluetooth.
2. Allow MIDI access in the browser. If the browser asks to connect to a MIDI device, allow access for TooLab. If you previously blocked it, use the site controls beside the address bar to review the permission, then reload the test. Browser permission labels vary, so look for MIDI device access rather than microphone access.
3. Try another USB port or cable. Connect directly to the computer instead of through a hub. If possible, test a known working cable and port. A keyboard that uses a detachable cable can appear connected while still losing data through a damaged cable.
4. Close other music software. Quit the digital audio workstation, virtual instrument, or other browser tabs using the keyboard, then test again. Another program can affect whether the device is available to the browser.
5. Check whether the computer sees the device. On Windows 11, right-click Start and open Device Manager, then look under the sound or USB device lists for the keyboard. On a Mac, open Audio MIDI Setup and inspect the MIDI Studio window. If the keyboard is absent there too, focus on the cable, port, Bluetooth pairing, or keyboard itself.
6. Restart the browser and computer. This can clear a device connection that has stopped responding. Reopen the test in Chrome or Edge and grant MIDI access again if prompted.

When the keyboard may be faulty

If the same key fails when pressed alone on more than one computer, or several keys consistently fail in the same combinations after you have tried a direct connection, the keyboard may have a key or scanning fault. If it is new or under warranty, record which keys fail and contact the seller or manufacturer before opening it. For an older keyboard, compare the cost of repair with a replacement before arranging service.

What this check cannot tell you

MIDI carries instructions such as which note was pressed and released. It does not carry the sound of the piano or synthesizer itself. A MIDI Test can show whether those instructions reach the browser, but it cannot confirm how many notes a software instrument can play, how the instrument sounds, or whether a classroom audio system is working. After the browser check passes, play the lesson's main chords in the actual music app.