MIDI Test: Check Any MIDI Device Online in Your Browser
Overview
MIDI Test. The MIDI Test puts your connected MIDI keyboard or controller on screen — click Enable MIDI Access, then play a note and watch it light up on the on-screen keyboard while the Last Note, Velocity, and raw message log capture every note-on, note-off, and CC message as it arrives. It needs a Chromium browser such as Chrome or Edge, since Safari and Firefox don't support the Web MIDI API without an experimental flag. The online microphone check runs entirely in your browser via the Web Audio API — nothing is uploaded anywhere.
Plug in a MIDI keyboard or MIDI controller, open this MIDI test in a compatible browser, and press anything: you see every message the device sends before your music software or audio engine gets involved. It is the fastest way to test your MIDI setup and settle whether a problem lives in the hardware or in the software chain behind it.
What a MIDI Test Shows You in Real Time
A MIDI test never plays sound itself. It reads the raw MIDI data your instrument sends and prints it in real-time, across the full range of 88 keys. Run the android mic test online to see exactly what's working and what isn't.
Note Detection, Note On/Off and Velocity Values
Note detection turns each key press into a note on/off pair, showing pitch names such as E3 next to the note number. Each Note On carries a strength from 0 to 127. Play the same key softly and then hard and the reading should rise smoothly; the min, average and max statistics make dead or unresponsive keys stand out, because one key reads far lower than its neighbours.
Control Change, Pitch Bend and Aftertouch in the MIDI Log
Knobs, faders and the mod wheel are continuous controllers. Each CC message carries one of 128 controller numbers plus a value, so the MIDI log tells you which control sent which CC data. The pitch bend wheel is the exception: it sends a 14-bit value from two data bytes, centred at 8192. Hex view shows the raw bytes, and the status byte reveals the MIDI channel.
| Message | Status (channel 3) | Data |
|---|---|---|
| Note On / Note Off | 92 / 82 | note 0-127, strength 0-127 |
| Control change | B2 | controller 0-127, value 0-127 |
| Bend | E2 | LSB + MSB, 0-16383 |
| Channel aftertouch | D2 | pressure 0-127 |
| Clock / Active sensing | F8 / FE | none |
Clock and active sensing flood the log, so filter them out. SysEx (system exclusive) needs extra browser permissions before a page may send it.
Online MIDI Tester Support: Web MIDI API, Drum Pads and DAW Controllers
This free online MIDI tester runs on the Web MIDI API, which Chrome, Edge and Opera support; Firefox and Safari don't, so use a Chromium-based browser. Any class-compliant device is plug & play:
- keyboards of every size
- drum pads and pad grids
- control surfaces with transport controls and mixing surfaces
Keep the device connected before the page loads, allow MIDI access when asked, and try refreshing if nothing is detected. Some MIDI devices need drivers installed first.
Worked Example: One Key Press in the MIDI Monitor
To test the keyboard, press E3 at medium force on channel 3. The MIDI monitor logs 92 34 57: Note On, channel 3, note 52, strength 87. Note 52 is E3, whose frequency follows The free noise suppression test runs entirely in your browser via the Web Audio API — nothing is uploaded anywhere.
$$f = 440 \times 2^{\frac{n-69}{12}} = 440 \times 2^{\frac{52-69}{12}} \approx 164.81\ \text{Hz}$$
Next, nudge the wheel up: E2 00 5A. The value is \(90 \times 128 + 0 = 11520\), which sits 3,328 above centre. With a ±2 semitone range that is \(\frac{3328}{8192} \times 2 = 0.8125\) semitones, about +81 cents.
A sweep from E3 to B3 at the same force reads 87, 84, 91, 86 and 19: the weak B3 signal drags the average to 73.4, while the other four average 87.0. That one key needs cleaning or a sensor repair, not a computer fix.
Checking a Used MIDI Keyboard in the Tester Before You Pay
I'm at a seller's flat with a secondhand 61-key controller listed at $240, and I'm using this online tester's note and strength readings to decide whether to buy it, haggle, or walk away. Ten minutes of readings give the answer, and here it is up front: one key, F#5, reads at about 51% of its neighbours, so I offer less and budget for a repair.
My laptop runs Chrome, so I plug the keyboard in, allow MIDI access and play each key of the top octave three times at the same medium force. Most of them land between 77 and 84. F#5 doesn't:
| Key | Medium force (3 presses) | Average | Full force average |
|---|---|---|---|
| F5 | 80, 77, 82 | 79.7 | 121.0 |
| F#5 | 38, 44, 41 | 41.0 | 63.3 |
| G5 | 79, 83, 78 | 80.0 | 119.3 |
The rerun at full force is the cross-check that matters. A velocity curve setting scales every key the same way, so if the curve were the culprit, all three would move together. Instead F#5 holds the same ratio, 41.0 divided by the 79.8 neighbour average is 0.51 and 63.3 against 120.2 is 0.53, which points to a dirty or worn contact under that one key. It also caps out at 63, so it can never reach the loudest sample layers that start near 100 on most pianos.
Two things I deliberately don't count as faults. Several keys send a Note On with strength 0 when released; the MIDI 1.0 specification treats that as a Note Off, so the log is normal. The bend wheel rests at 8,064 instead of the 8,192 centre, a drift of 128 steps, or \(\frac{-128}{8192} \times 200 = -3.1\) cents at a ±2 semitone range. That sits under the roughly 5-cent difference most listeners can hear, though recording software may still log it as constant bend data, so I'd add a small dead zone in the software.
The number to watch is the full-force reading on the weak key: if cleaning the contact strip doesn't lift it above 100, the strip needs replacing. I offer $200, and after cleaning I rerun the same three-press check on F#5 in the tester: a full-force reading above 100 means the repair worked.
How to Test a MIDI Device on Windows and macOS
Offline, use a desktop monitor app. The MIDI output test needs a loop back to an input, since monitors read incoming messages only.
Checking MIDI Input in MIDI-Ox on Windows
- Close other audio and MIDI software, then open MIDI-Ox.
- In Options > MIDI Devices, tick only your device's ports under MIDI Inputs and MIDI Outputs.
- Play the keyboard: incoming MIDI data should scroll in the window.
Audio MIDI Setup Status Lights on a Mac
- Open the app from Utilities and choose Window > Show MIDI Studio.
- Select the device and click the Test MIDI Setup button; a MIDI interface flashes the status lights on its ports.
- Play a note: the up arrow for that MIDI out port highlights when the Mac receives it.
The free MIDI Monitor app does the same job, listing every port under Sources.
Reading Your MIDI Data Results
What you see tells you where the device stops communicating.
Data Appears in the MIDI Monitor
The device and computer are talking. If a virtual instrument still stays silent, the software settings in your DAW were never set up, or have drifted.
Only Some Keys Reach the MIDI Monitor
Missing keys, wrong notes or parameters on the wrong channel point to hardware. Check the user manual, then contact technical support.
No Data: Check the USB Cable and Input Source
- Swap the cable and try another USB port.
- Make sure the device is connected and listed as an input source.
- Select every port; a keyboard may send extra data on a second one.
If the MIDI device still isn't communicating, follow the maker's troubleshooting guide.
No Sound from MIDI Sound Modules After a MIDI Setup Check
If the tester shows incoming notes but you hear nothing, the MIDI side works and the fault is further down the chain. If the interface lights flash but the module stays silent, run a lead from a MIDI Out on the interface to its MIDI In. Then make sure its audio outputs are connected to a mixer or speakers, or plug headphones in to hear it directly.
Frequently Asked Questions
- Which browsers can run an online MIDI test?
- Chrome, Edge and Opera support the Web MIDI API, so they can read your device directly. Firefox and Safari don't, so switch to a Chromium-based browser if nothing appears.
- Why isn't my MIDI device detected?
- Connect the device before you open the page, allow MIDI access when the browser asks, and refresh if it still isn't listed. Some devices need a driver installed first, and another MIDI app holding the port can block it too.
- What is a CC message?
- A Control Change message comes from knobs, faders, the mod wheel and other continuous controllers. It carries a controller number from 0 to 127 and a value from 0 to 127.
- Can a MIDI tester check MIDI output?
- A monitor only reads what arrives at an input. To check an output, loop it back into an input with a cable or a virtual port, or use your DAW or your computer's MIDI setup tool.
- Data shows in the monitor but my software makes no sound. What now?
- The device and computer are communicating, so the problem is the software setup: pick the device as an input in your DAW, arm the track and check the virtual instrument's MIDI channel.
- Only some keys or knobs respond. Is the keyboard faulty?
- If the same keys stay silent or send the wrong notes in the monitor too, the hardware is likely at fault. Check the user manual for settings first, then contact the maker's technical support.
- Why do I see a Note On with velocity 0 when I release a key?
- The MIDI specification lets a device send Note On with velocity 0 instead of Note Off. It means the key was released and is not a fault.