This open-source MIDI tool allows you to monitor all incoming MIDI messages from your selected devices and send custom MIDI messages to any connected output device, including Note, Control Change (CC), Clock, Program Change (PC), SysEx (System Exclusive), and more.
All MIDI data is processed locally in your browser—nothing is sent or stored anywhere else.
You can export your log using the Export button—choose to export all columns (press 1) or only raw MIDI messages (press 2). The Filters button lets you select which message types and channels you want to see in the log. Use the "Show last" box to limit how many recent messages are displayed. The button in the Raw Message column lets you toggle between hexadecimal and decimal display for message data.
Supported browsers include Google Chrome, Edge, and Firefox (experimental). If you do not see your MIDI device, please ensure permission is granted, the device is connected and not in use by another application, then refresh the page.
After connecting a new device, use the Refresh Devices button to update the device list.
To monitor, select one or more MIDI input devices (hold Ctrl/Cmd to select multiple) and press Connect. To send messages, select a MIDI output device and use the Send button.
You can disconnect inputs at any time by clicking Disconnect.
Enable Auto Scroll to keep the latest messages in view.
Piano Roll:
The Piano Roll displays recent MIDI notes visually as bars, where the length of each bar represents the duration of the note and the color indicates its velocity (intensity).
You can adjust how many seconds of note history are shown, and set the minimum and maximum note range to change the scale.
Both Note On and Note Off events are recorded and displayed as bars.
Hovering your mouse over a note bar will show its velocity and note value.
You can pause or resume the Piano Roll display at any time using the Pause button.
CC Analyzer:
The CC Analyzer lets you select up to 4 different MIDI Control Change (CC) numbers and view their recent values as colored bar graphs.
Each CC is shown in a separate color, and the most recent values are displayed as bars, making it easy to monitor real-time changes.
Hovering your mouse over a bar will show the exact CC number and value.
You can clear the graph at any time, and select which CC numbers to display using the dropdown menu.
MIDILLI Tech