Web MIDI Keyboard Tester - Online Visual Note Display

A MIDI Keyboard Tester is an online diagnostic tool that captures MIDI (Musical Instrument Digital Interface) signals from your keyboard or controller and displays them visually in real-time. When you press a key, the tool shows the note name (e.g., C4, F#3), MIDI note number (0–127), velocity (how hard you played, 1–127), and the calculated frequency in Hertz. The virtual piano keyboard highlights pressed keys, making it easy to verify that all keys, sensors, and MIDI channels are functioning correctly—perfect for musicians, producers, and technicians troubleshooting their gear.

Step 1: Connect your MIDI keyboard to your computer via USB (or use a MIDI-to-USB interface for 5-pin DIN devices).
Step 2: Click the "Connect MIDI" button. Your browser will prompt for permission to access MIDI devices.
Step 3: Select your device from the dropdown menu (or keep "All MIDI Devices" selected).
Step 4: The status indicator will turn green when connected. Play any key and you'll see instant visual feedback.
Note: This tool requires Google Chrome, Edge, or Opera with HTTPS enabled. Firefox supports Web MIDI via a flag in about:config.

Common reasons include: (a) Your browser doesn't support the Web MIDI API (only Chrome, Edge, and Opera support it natively). (b) The site is not served over HTTPS or localhost—Web MIDI requires a secure context. (c) The MIDI driver for your keyboard isn't installed (check your manufacturer's website). (d) The USB cable or port is faulty—try a different cable or port. (e) You denied the browser's MIDI permission prompt—reset it in your browser's site settings. (f) Some devices need to be powered on before launching the browser.

Yes! You can click directly on the virtual piano keys with your mouse or tap them on a touchscreen. The tool will simulate MIDI note-on and note-off events with a default velocity of 100. This is great for testing the visual display, learning note names, or understanding how the tool works before connecting real hardware. The virtual keyboard spans from C3 (MIDI 48) to B5 (MIDI 83), covering three full octaves.

As of 2024, Google Chrome (version 43+), Microsoft Edge (version 79+), and Opera (version 30+) fully support the Web MIDI API. Firefox has partial support hidden behind a flag—navigate to about:config and set dom.webmidi.enabled to true. Safari on macOS and iOS does not support Web MIDI at this time. Always ensure you're on a secure connection (HTTPS) as the API is blocked on plain HTTP for security reasons.

MIDI velocity measures how hard or fast a key is pressed, ranging from 1 (softest) to 127 (hardest). A velocity of 0 is treated as a note-off event. In this tool, the velocity is visualized as a colored bar beneath each active note—green for low velocities (1–40), blue for medium (41–80), and gold for high velocities (81–127). Velocity is crucial for expressive playing and is used by virtual instruments to determine volume, timbre, and articulation.

Frequencies are calculated using the standard equal temperament formula: f = 440 × 2(n−69)/12, where n is the MIDI note number and A4 = 440 Hz (MIDI note 69) is the reference pitch. For example, MIDI note 60 (C4, middle C) yields 261.63 Hz. Each semitone step multiplies the frequency by the 12th root of 2 (≈1.05946). The tool displays this frequency in real-time for every active note.

Absolutely. All MIDI data processing happens entirely within your browser using the Web MIDI API. No MIDI data is ever sent to any server, recorded externally, or shared with third parties. This tool is a purely client-side application—your keystrokes, velocities, and device information remain 100% local to your computer. You can verify this by disconnecting your internet after the page loads; the tool will continue to function normally.

The tool monitors all 16 MIDI channels (0–15) simultaneously. When a note is played, the channel number is extracted from the MIDI status byte and displayed in the status bar. MIDI channels allow a single device to control multiple instruments independently—each channel can carry its own stream of note and controller data. The channel display updates dynamically as notes arrive from different channels.

Yes! The tool listens for MIDI CC 64 (sustain pedal). When the pedal is pressed (value ≥ 64), a pedal indicator lights up in the header, and notes will remain visible even after their physical keys are released—just like a real piano sustain pedal. When the pedal is released (value < 64), all sustained notes are cleared. This allows you to test both keyboard and pedal functionality in one place.