A Voice for Your App — No Internet Required

A voice that lives on your machine

Imagine you're building a small app — a menu reader for your restaurant, a client portal for your agency, maybe just a tool that reads back your emails while you're cooking. You want it to speak. The usual path is to pay for a cloud service, hand your text over to someone else's servers, and hope the bill stays manageable.

Supertonic 3 is a different idea. It's a free, open-source engine that converts text to speech entirely on your own computer. No internet connection once it's set up. No API key. No monthly invoice. The audio it produces is genuinely good — 44.1kHz, the same quality you'd hear on a podcast — and it works in 31 languages, including Spanish, French, Japanese, and Arabic.

What makes it interesting for builders is something quieter: if you already use an app that talks to OpenAI's voice service, you can point it at Supertonic instead with almost no changes. It speaks the same language, technically speaking. So your costs drop to zero and your data never leaves the building.

People are already using it inside reading apps, browser extensions, and local AI assistants. The project hit 10,000 enthusiastic followers on GitHub in under six months — not bad for something that asks nothing of your wallet.

If you've ever wanted to add a voice to something you're building — or you're paying for speech-to-text services and wondering if there's an alternative — this is worth keeping on your radar.

Words worth knowing

On-device — runs on your own computer, not on someone else's server far away. Your data stays with you.

Open-source — the code is public and free to use. No licence fees, no vendor to depend on.

API key — a kind of password that lets a service bill you for usage. No API key here means no bill.

44.1kHz audio — a measure of sound quality. It's the standard for music CDs. When a voice engine outputs at this level, it sounds natural rather than robotic.