Online MIDI Synthesizer — Connect and Play

How to Connect Your MIDI Keyboard

The connection has four parts: cable and power, browser support, explicit permission, then a detected input. Follow them in order. If you're still sorting out what MIDI is, readMIDI vs synthesizer: the actual differencefirst.

1. Plug in the keyboard. Connect your MIDI controller to a USB port on the computer. Direct ports beat hubs — a passive hub can under-power some controllers.
2. Check the MIDI panel. If the current browser does not expose Web MIDI, the panel says so and the on-screen keyboard remains available. Web MIDI requires a secure HTTPS page.
3. Choose Connect MIDI and approve access. Browsers may require explicit permission before listing connected devices. If you block access, use the site's browser settings to allow MIDI, then chooseRetry access. Permission controls differ between browsers.
4. Play a key. When the status bar reads "MIDI device connected: <your keyboard>", every key press plays the synth. Velocity and the sustain pedal (CC64) are already mapped.

On Windows

Many class-compliant controllers use built-in operating-system support. If the device isn't detected, check the model's driver requirements and try another data-capable USB port. Closing other MIDI apps can also help when the operating system allows only one active client.

On macOS

You can confirm a detected device on macOS in Audio MIDI Setup → Window → Show MIDI Studio. If a bus-powered controller does not power on, check the cable, adapter, and power path before changing browser settings.

What the MIDI Status Means

Web MIDI has limited browser availability and requires HTTPS plus explicit user permission. The live status above is more useful than a static browser list because it checks the browser you are using now. See theMDN Web MIDI referencefor current compatibility and security requirements.

Web MIDI only controls the external input path. Thekeyboard synthesizeralso supports computer-keyboard, mouse, and touch input where browser audio is available.

Troubleshooting: MIDI Not Working?

Start with the status shown above, then work through the matching recovery path. Permission, operating-system detection, power/cable issues, and browser support are separate layers.

1. Check the status bar first. It tells you which layer failed: "not supported" means the current browser or context; "blocked" means permission; "no device detected" means the browser is fine but can't see the hardware.
2. Re-open a denied permission. Clicked "Block" once by accident? Click the lock (or tune) icon left of the address bar → findMIDI devices → set to Allow → reload the page. The prompt won't re-appear on its own after a denial.
3. Confirm the OS sees the device. On Windows, open Device Manager and look for your controller under "Sound, video and game controllers" — a warning icon there means a driver or port issue, not a browser one. On macOS, open Audio MIDI Setup → Window → Show MIDI Studio and check the device appears.
4. Rule out the cable and port. Try a different USB port (directly on the machine, not a hub), and if the controller is bus-powered, watch whether its lights come on at all. Charge-only USB cables carry no data — a classic gotcha with USB-C cables.
5. Restart the browser. After checking permission and the cable, a full quit and relaunch can clear a temporary browser session issue.
6. Try another supporting browser. If nothing above helps, a clean browser profile can help distinguish site permissions or extensions from an operating-system or hardware problem.

Still nothing? Write us the controller model, your browser version, and what the status bar says — those details make the report actionable (see the contact page).

Low-Latency Tips for Online MIDI Synthesizers

Latency is the gap between striking a key and hearing it. This synth is built on the Web Audio API. The delay you hear varies with the browser, audio device, system load, and power settings. If you hear a lag:

• Compare a current supporting browser if the delay is clearly audible.
• Close heavy tabs (video calls, streaming, other audio apps) that compete for the audio device.
• Plug the controller straight into the computer; skip unpowered USB hubs.
• On laptops, compare plugged-in operation; aggressive power saving may add delay.
• Keep the synth tab in the foreground; browsers deprioritize background tabs.
• If timing is critical, compare the result with your DAW and audio-interface setup; this page does not expose an audio buffer control.

Sounds to Try with a MIDI Keyboard

With real keys under your fingers, these presets get out of the way and let you play. Each button loads the sound and plays its demo phrase above — then take over on your controller.

Looking for the everything-free rundown instead? Thefree synthesizer page lists every feature you get without an account. And if you're still deciding whether to buy a controller at all, our guide toplaying piano on your computer keyboardcovers exactly when the upgrade is worth it.

Last verified: 2026-09-21 — permission and compatibility wording checked against MDN and Chrome's Web MIDI permission documentation.