About Online Keyboard Synth

A free browser synthesizer built by one person who plays with synthesizers — honest about what it is and what it isn't.

Last verified: 2026-09-04

Who maintains this site

Hi, I'm Milo Kessler. I built Online Keyboard Synth because of a very ordinary moment: I was away from my MIDI keyboard, had a melody stuck in my head, and every "online synthesizer" I found either wanted my email, buried the keys behind a loading spinner, or ignored my computer keyboard entirely. So I built the page I wanted to find — one where you press a letter key and hear a synth before you've finished reading the title.

I'm not a classically trained audio engineer, and I won't pretend otherwise. I'm a web developer and a hobbyist synth player who cares about the details: the key letters are printed on the piano because I kept forgetting the mapping myself, the recorder exists because ideas evaporate, and the MIDI status bar exists because "is this thing even connected?" should never be a mystery. If something on this site doesn't work the way this page claims, tell me through thecontact page — those reports get fixed first.

What this site is

Online Keyboard Synth is an independent, one-person project: a free online keyboard synthesizer that runs entirely in your browser. It plays from your QWERTY keyboard, a USB MIDI controller, a mouse, or a touch screen; it shapes sound with real oscillators, a resonant filter, an ADSR envelope, and effects; and it records your playing to files you own.

What this site is not

It is not a DAW replacement, not a sample library, and not a subscription funnel wearing a free costume. There is no account system, no upload, no tracking of what you play. The sound engine is the Web Audio API in your browser; recordings are encoded on your device.

How the site is kept honest

• Every feature mentioned in the text is live in the tool on the same page — the copy is written against the working instrument, not a wishlist.
• Browser compatibility notes are checked against caniuse.com and re-verified when browsers change.
• The synth's core math (key mapping, note frequencies, envelope timing, WAV encoding) is covered by automated unit tests that run on every build.
• No invented ratings, review counts, or user numbers — you'll find none anywhere on this site, in the text or in the metadata.

Contact

Questions, corrections, or a preset you think should exist:hello@onlinekeyboardsynth.com, or thecontact form.