Free Online Piano

What is Synthio?

A free online synthesizer you can play directly in your browser — no downloads, no plugins required. It uses the Web Audio API to generate sound in real time.

Play with your keyboard, mouse, a MIDI controller, or tap the keys on a touchscreen. Slide across keys to glide between notes.

Keyboard Shortcuts — Octave 1

Keyboard Shortcuts — Octave 2

Pitch Bend

Slides pitch up or down by up to ±2 semitones and springs back to centre on release.

• Bend Wheel — the dark vertical strip to the left of the keyboard. Drag up to bend up, drag down to bend down.
• Arrow Keys — hold ? to bend up, hold ? to bend down. Release to spring back.
• MIDI Pitch Wheel — hardware pitch wheel is read in real time with full 14-bit resolution once connected.

Controls

• Preset — Synth uses the oscillator engine. Grand Piano, Rhodes, Wurlitzer, and Organ use real sampled recordings. Waveform and Detune are disabled for sampled instruments.
• Volume — master output level. Affects all playing notes instantly.
• Waveform — (Synth only) Sine is smooth, Square is buzzy, Sawtooth is bright and rich, Triangle is mellow.
• Octave — shifts all keys up or down an octave. Use - / = keys on your keyboard.
• Attack — how long it takes for a note to reach full volume after pressing a key.
• Decay — how quickly the volume drops after the attack peak.
• Sustain — the volume level held while a key is pressed.
• Release — how long the note fades out after you release the key.
• Cutoff — lowpass filter frequency. Lower values make the sound warmer and more muffled.
• Res — filter resonance. Higher values add a sharp peak at the cutoff frequency.
• Detune — (Synth only) a slightly detuned second oscillator layered on top, adding thickness and warmth.
• Low Cut — removes low frequencies below the set value. Useful for cleaning up bass rumble.
• Reverb — adds a room or hall effect. Higher values make the sound feel more spacious.

MIDI Setup

• Desktop (Chrome / Edge) — plug in your MIDI controller via USB and click Connect MIDI. It is detected automatically.
• Pitch Wheel — the hardware pitch wheel on your controller works automatically once connected.
• Knobs (CC 14–17) — CC 14, 15, 16, 17 map to Cutoff, Resonance, Detune, and Low Cut respectively.
• Android — in Chrome go to chrome://flags, enable Web MIDI API, relaunch, then connect via USB OTG adapter.
• iPhone / iPad — use a Lightning or USB-C to USB adapter. Safari on iOS supports Web MIDI natively.
• Bluetooth MIDI — works on iOS with compatible controllers. Android support varies by device.

Mobile Tips

• Rotate to landscape for the best experience — the full 25-key keyboard fits on screen.
• Tap keys to play. Multiple fingers work at once (polyphonic). Slide across keys to glide between notes.
• Tap Settings (top-right) to adjust all controls. Tap ? to hide the browser UI.
• On Android, Add to Home Screen for true fullscreen.