Free browser-based MIDI diagnostic tool (Velocity, Aftertouch, CC)

[lukeio]

[UPDATE: Mar 7, 2026 - Major "Pro" Update Released! ]
Massive thanks to the community feedback. I've just added:

Full SysEx Support (Receive, Monitor, Save dumps, and Send custom Hex)

Hardware MIDI Routing (IN to OUT passthrough)

Virtual Keyboard to send notes

Hex view & Clock/FE message filters
(See my latest reply below for full details)

-------------------------------------------------------

Hey everyone,

I’m an independent developer working on a web-based testing suite for hardware controllers. I recently expanded it with a dedicated MIDI section using the Web MIDI API, and thought it might be useful here for troubleshooting and hardware evaluation.

It runs entirely in the browser (Chrome/Edge) with no installation, no login, and no ads. All data stays local.

You can try it here:
https://controllertest.io/midi-tester/

Main features:

88-key visual layout

Real-time velocity, pitch bend, and aftertouch monitoring

CC monitor & detailed MIDI event log for inspecting raw data

I mainly use it to quickly check for dead keys on second-hand keyboards or verify what CC messages a knob is sending, without launching a full DAW session.

Curious to hear how it behaves with different hardware setups, or if there are features that would make it more useful.

Cheers!
 

[djvd]

Thank you!

[aMUSEd]

...or if there are features that would make it more useful.

Could MIDI 2 functionality testing be added please?

[lukeio]

...or if there are features that would make it more useful.

Could MIDI 2 functionality testing be added please?

I'd love to! Unfortunately, we are currently limited by browser tech. The Web MIDI API in Chrome/Edge only supports MIDI 1.0 data streams right now and can't read MIDI 2.0 Universal MIDI Packets (UMP) natively.

Once browsers update the API to support the new MIDI 2.0 specs, I will absolutely add a dedicated MIDI 2.0 testing module.

What MIDI 2.0 gear are you rocking right now?

[aMUSEd]

...or if there are features that would make it more useful.

Could MIDI 2 functionality testing be added please?

I'd love to! Unfortunately, we are currently limited by browser tech. The Web MIDI API in Chrome/Edge only supports MIDI 1.0 data streams right now and can't read MIDI 2.0 Universal MIDI Packets (UMP) natively.

Once browsers update the API to support the new MIDI 2.0 specs, I will absolutely add a dedicated MIDI 2.0 testing module.

What MIDI 2.0 gear are you rocking right now?

That's the problem really - I have a NI Kontrol MkIII keyboard that is meant to support MIDI 2 but it doesn't seem to work properly but NI say the problem is host support isn't there either, and that may also be true - certainly Logic MIDI 2 mode also doesn't seem to work properly. So to be able to separate one problem from the other by testing the keyboard would be useful.

[lukeio]

...or if there are features that would make it more useful.

Could MIDI 2 functionality testing be added please?

I'd love to! Unfortunately, we are currently limited by browser tech. The Web MIDI API in Chrome/Edge only supports MIDI 1.0 data streams right now and can't read MIDI 2.0 Universal MIDI Packets (UMP) natively.

Once browsers update the API to support the new MIDI 2.0 specs, I will absolutely add a dedicated MIDI 2.0 testing module.

What MIDI 2.0 gear are you rocking right now?

That's the problem really - I have a NI Kontrol MkIII keyboard that is meant to support MIDI 2 but it doesn't seem to work properly but NI say the problem is host support isn't there either, and that may also be true - certainly Logic MIDI 2 mode also doesn't seem to work properly. So to be able to separate one problem from the other by testing the keyboard would be useful.

Exactly this! That "hardware blames the DAW, DAW blames the hardware" loop is a nightmare.

Having a neutral, standalone tool just to see the raw output and figure out who is actually dropping the ball is exactly why I build these testers. The Kontrol MkIII is an awesome board, and it's super frustrating that the browser API can't help you isolate the problem just yet.

[Phil999]

thank you for sharing this web app.

When choosing the MIDI device, the dropdown menu may be cut off at the bottom. So when the computer has many MIDI ports, especially virtual ones, the lowest in the list may not be possible to be selected. A solution would be to have a scroll bar in this dropdown menu.

[Constructed Identity]

This could be a really nice replacement for MIDI OX, the tool I think most of us have used to send/ receive MIDI dumps.
So, if you haven’t already, add I nice MIDI sysex receive/send section.

[lukeio]

thank you for sharing this web app.

When choosing the MIDI device, the dropdown menu may be cut off at the bottom. So when the computer has many MIDI ports, especially virtual ones, the lowest in the list may not be possible to be selected. A solution would be to have a scroll bar in this dropdown menu.

You were totally right about the dropdown menu getting cut off. I completely overhauled the connection panel. You can now independently select specific 'IN' and 'OUT' devices with a proper scrollbar. No matter how many virtual cables you have, scrolling through them is buttery smooth now. Thanks for the heads-up!

[lukeio]

This could be a really nice replacement for MIDI OX, the tool I think most of us have used to send/ receive MIDI dumps.
So, if you haven’t already, add I nice MIDI sysex receive/send section.

Saying this could replace MIDI-OX is a massive compliment, and I took it as a serious challenge! I've just rolled out a major update specifically for power users like you.

Right out of the box when you connect, you now get a full DAW-like testing experience:

Hardware Routing (MIDI Thru): Route your input device directly to your selected output (like a virtual MIDI patchbay).

Virtual Keyboard: Click the piano UI to send notes directly to your selected Output device.

Raw Hex Event Monitor: Toggle the main right-hand log between "Readable" text and raw "Hex".

Message Filters: Easily filter out those annoying Clock (F8) and Active Sensing (FE) signals.

Regarding SysEx Dumps (Receive, Monitor & Save):
Because SysEx dumps can be massive, I built a completely separated workflow for it in the main column to keep the UI clean:

Dedicated SysEx Log: Right below the "Playing Notes" card is an independent SysEx area. You can passively receive and monitor your hardware dumps here. To keep the browser running smoothly, large payloads are smartly truncated in the UI, but you can click the download icon to save the full .syx dump file to your computer!

SysEx Send Terminal: Right below that log is the terminal for sending custom hex commands. To keep casual users safe, I locked this sending terminal behind an "Enable SysEx" safety toggle.

I'd be absolutely thrilled if you could give it a spin and see if it meets your "MIDI-OX replacement" standards!

Also, I just added a Discord community (link in the top nav). If you find any bugs with your hardware dumps or have more hardcore feature requests, come hang out with us!

[Phil999]

I completely overhauled the connection panel. You can now independently select specific 'IN' and 'OUT' devices with a proper scrollbar. No matter how many virtual cables you have, scrolling through them is buttery smooth now. Thanks for the heads-up!

that was quick. Good work.

[Constructed Identity]

This could be a really nice replacement for MIDI OX, the tool I think most of us have used to send/ receive MIDI dumps.
So, if you haven’t already, add I nice MIDI sysex receive/send section.

Saying this could replace MIDI-OX is a massive compliment, and I took it as a serious challenge! I've just rolled out a major update specifically for power users like you.

Right out of the box when you connect, you now get a full DAW-like testing experience:

Hardware Routing (MIDI Thru): Route your input device directly to your selected output (like a virtual MIDI patchbay).

Virtual Keyboard: Click the piano UI to send notes directly to your selected Output device.

Raw Hex Event Monitor: Toggle the main right-hand log between "Readable" text and raw "Hex".

Message Filters: Easily filter out those annoying Clock (F8) and Active Sensing (FE) signals.

Regarding SysEx Dumps (Receive, Monitor & Save):
Because SysEx dumps can be massive, I built a completely separated workflow for it in the main column to keep the UI clean:

Dedicated SysEx Log: Right below the "Playing Notes" card is an independent SysEx area. You can passively receive and monitor your hardware dumps here. To keep the browser running smoothly, large payloads are smartly truncated in the UI, but you can click the download icon to save the full .syx dump file to your computer!

SysEx Send Terminal: Right below that log is the terminal for sending custom hex commands. To keep casual users safe, I locked this sending terminal behind an "Enable SysEx" safety toggle.

I'd be absolutely thrilled if you could give it a spin and see if it meets your "MIDI-OX replacement" standards!

Also, I just added a Discord community (link in the top nav). If you find any bugs with your hardware dumps or have more hardcore feature requests, come hang out with us!

MIDI-OX has been around for so long it is a standard and everyone from Matt Johnson to me uses it to make backups of their synthesizer's patch memory before traveling with their keyboards. But its U.I. is from 2002 and it could certainly be replaced.
I will test out your software and let you know if I trust it enough.