Cynth sends files and folders of any size straight between your devices and the people you trust. No upload links. No size limits. End-to-end encrypted.
Free during early access. One email when it's ready for your platform — nothing else.
$ cynth send ./footage.mov → arrives on your other device, directly
Cynth connects your devices the fastest safe way it can, in priority order. You never pick; it just takes the most direct route available.
Your devices find each other and transfer at local-network speed. Nothing leaves your network.
Behind NATs, devices punch a direct hole through and connect peer-to-peer, coordinated by the signaling server.
Frames fall back through a relay that forwards ciphertext only. Slower, still private — the relay never sees your files.
Send a screenshot or a 400 GB project. No caps, folder structure intact.
Connection drops mid-transfer? It picks up exactly where it left off.
Pair your own machines and send to the people you trust. No account needed to move between your own devices.
Windows, macOS, iOS, Android, and Linux — the same guarantees everywhere, on a shared core engine.
Local speed when it can, a direct link when it can't, an encrypted relay only as a last resort.
Fast, modern transport with mutual-TLS authentication between devices.
Every connection is authenticated both ways with mutual TLS, using certificates derived from a per-device Ed25519 identity key. Your files travel directly between devices; when a direct path is impossible, they fall back through a relay that only ever forwards ciphertext. There's no upload step and no server-side copy — your data lives only on your devices.
Cynth is in active development. Join the list and you'll get one email when it's ready for your platform.
The files you own shouldn't have to pass through someone else's computer to reach your own.
You have a file here and you want it there — on your other device, or with someone you trust. The modern answer is to upload it to a company's servers, wait, get a link, and hope the size cap holds. A private handoff, turned into a transaction on infrastructure you don't control.
The middleman isn't a law of physics — it's a business model. Devices on one network find each other directly. Devices behind routers punch a direct path through. And when a direct path is impossible, a relay can carry the traffic without ever reading it. Cynth is built around one refusal: it won't become a copy of your files on a server you don't own.
The name is short for Cynthia — the moon goddess, whose silver arrow flies straight — and a tribute to my wife, Cindy. The metaphor just happened to fit.