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Play, parse, and debug MIDI files or hex data online. Features event log analysis and instant music playback to assist in music production and development.
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Overview
Understand what the tool solves, how it works, and the boundaries of its data.
This page monitors MIDI input from connected devices that the browser can access. It lists available input and output ports, then records incoming messages with a timestamp, source name, event label, and raw data bytes. MIDI carries instructions and control events, such as note and controller messages; it is not recorded sound. The MIDI Association describes MIDI as a way for instruments and other devices to exchange musical notes, program changes, and expression control. MIDI Association: MIDI 1.0 Detailed Specification (checked 2026-09-28).
The Web MIDI API lets a web page request access to MIDI devices, subject to browser support and permission. Its specification requires a secure context for the access method and describes permission handling. W3C: Web MIDI API (checked 2026-09-28). This tester displays the events it receives; it does not load a Standard MIDI File, transmit a message, or produce audio.
Note On and Note Off indicate note-start and note-release message types. For those events the log also shows the note number and velocity value sent by the device. Control Change, Program Change, Pitch Bend, channel pressure, and polyphonic key pressure identify other message families. The raw bytes are shown as decimal numbers, which can help when comparing a device’s output with a MIDI reference. A timestamp orders received events; it is not an audio-latency measurement.
The log keeps the most recent 50 entries, with new messages at the top. The device may send different event types depending on its controls and configuration.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Connect a MIDI keyboard, pad, or controller and make sure the operating system recognizes it.
Open the page in a browser and allow MIDI access if prompted. Check whether the device appears under inputs.
Press and release one key. Look for Note On and Note Off entries, then compare the note number and velocity fields.
Move one knob, slider, pitch wheel, or pedal at a time. Watch for a new event label and raw byte sequence.
Repeat an action if needed and compare the incoming records. Use another MIDI monitor or your music software to investigate behavior beyond the messages shown here.
Use cases
See how the tool fits into real work and everyday tasks.
Test a few keys and their releases to see whether the browser receives corresponding note events from the selected controller.
Move a fader or pedal and inspect whether the device sends a control event. The log can help identify that an event arrived before checking its mapping in a music application.
Q&A
Find concise answers to common questions and confusing cases.
Check the physical connection and operating-system device list, then confirm that the browser supports MIDI access and that permission was granted. A device can be connected but unavailable to the page.
No. It confirms that a note message reached the browser. Sound requires a separate instrument or audio system, which this page does not provide.
The controller may send a different message, be configured on another device, or not transmit for that control. The page only lists messages it receives.
No. They help order received events; they do not measure USB, MIDI, or audio output latency.
Notes
Review scope, result limitations, and important precautions before use.
The log shows messages received in this browser session, not whether a controller is physically healthy or whether downstream software will interpret it as expected. Browser support, device availability, operating-system configuration, and access permission all affect what can be observed. Output ports may be listed, but this page does not send messages to them. Only the newest 50 received events remain visible, so older entries can roll out of the log.
Related
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