Phone to computer
One QR code, and the file goes from one device to the other without passing through a server.
Your files go from device to device, never through our serversShow a QR code on this device and scan it with the other one’s camera: the two connect directly and you exchange files in both directions. The files go through no server.
How to transfer a file from one device to another, step by step
The two devices connect directly to each other (WebRTC) thanks to a QR code; the file never passes through a server.
Show the QR code on one device
Click "Show the QR code". An encrypted invitation is deposited on Vellum’s pairing relay, valid for five minutes.
Scan the code with the other device
The camera is enough: the link opens the page directly, retrieves the invitation, then clears the key from the address bar once it has been used.
Wait for the direct connection
Each device asks a STUN server for its public address; the two then exchange their addresses through the encrypted relay and establish a direct WebRTC connection. With no traffic relay server (TURN), some company or mobile networks block this step; the same Wi-Fi almost always works.
Drop in the files to send
Once "The two devices are connected" is shown, drag in or pick the files; they go out in 16 KB chunks straight to the other device, in both directions at once if needed.
Check and save the received file
At the end of the transfer, the recomputed SHA-256 checksum confirms the file is intact; the "Save" button only appears once that check has passed.
The witness shown at the bottom of the page reports the number of requests sent to the relay and their encrypted weight: the files themselves make up none of it, not one byte.
Frequently asked questions
Does the sent file pass through a Vellum server?
No. Once the two devices are connected, the file flows directly between them over a WebRTC connection; it never goes through vellumpdf.ch. Only two small pairing messages (the connection offer and answer, a few kilobytes) pass through our relay, just long enough for the two devices to find each other.
What does the pairing server see?
Nothing readable. Both messages are encrypted with AES-GCM in your browser before being deposited, with a key that travels only in the QR code, after the `#` in the address — a part a browser never sends to a server. The relay keeps these unreadable bytes for five minutes at most, with no database and no log.
Why does the transfer fail on some networks?
Each device asks a Cloudflare STUN server for its public address to attempt a direct connection. Without a traffic relay server (TURN), some company or mobile networks still block that direct connection. The error message says so and suggests putting both devices on the same Wi-Fi network.
Is there a size or file-type limit?
No file type is refused. The practical limit is the device’s memory: the file is read entirely into memory before sending, so a large file can fail on a less powerful device, especially a phone.
How can I tell the received file is intact?
The sending device computes the file’s SHA-256 checksum and announces it at the end of the transfer; the receiving device recomputes the same checksum and compares it. A mismatched checksum or an incomplete file is flagged as such, never shown as successfully received.