Why a camera instead of an account
Every other way of getting a link onto your phone goes through somebody else’s computer. Messaging it to yourself puts it in a chat log. A clipboard that syncs puts it on a server, which is exactly the wrong place for the things people most often move this way — a wifi password, a one-time code, an internal address, a long API key.
A screen and a camera are already a channel, and they are a channel nobody else is on. That also makes this work where the alternatives cannot: two devices on different networks, a laptop with no internet, a phone with no signal, a machine that is deliberately not connected to anything.
What happens when the text is too long for one code
A QR code a phone can read across a desk holds a few hundred characters. People paste more than that, so anything longer is cut into numbered pieces and the sending screen cycles through them. The receiving side collects pieces until it has the set — in whatever order the camera happens to catch them, however many times it sees the same one, and over as many passes as it takes. The bar fills as they arrive.
Each piece carries which send it belongs to, so the previous message still sitting on the sender’s screen cannot get mixed into this one. The whole message carries a checksum, so a set that looks complete but is not gets rejected rather than handed over half wrong.
Getting a clean read
Fill the camera frame with the code rather than the whole screen, and hold it still enough that one code is on screen for a whole camera frame. If the pieces are arriving slowly, turn the speed down — fewer codes per second means each one is up long enough to be caught, and the total time usually goes down rather than up.
Screen brightness matters more than resolution. A dim screen photographed at an angle is the usual reason a code will not read, and it is fixed by tilting the screen rather than by moving the phone closer.
Frequently asked questions
Does the text go over the internet?
No. It is drawn on one screen and read by the other camera, and nothing is sent anywhere at all. The page keeps working with both devices offline, which is the clearest way to see that no server is involved.
How much text can it carry?
There is no hard limit, but time grows with length. Up to about two thousand characters crosses in a few seconds. Much beyond that and it is worth asking whether a file would be easier than a clipboard.
Can I send it the other way, from phone to computer?
Yes. Both sides of this page do both jobs — show the code on the phone and point the computer’s webcam at it. A webcam is usually a worse camera, so hold the phone closer than feels necessary.
Is it safe for a password?
The text never leaves the two devices, so there is nothing to intercept in transit. What is on screen is visible to anyone who can see the screen or a camera pointed at it, so the caution is the same as reading it aloud.
The camera will not start.
A page can only use the camera over HTTPS and only with permission. If the prompt was refused once, most browsers remember that — the padlock in the address bar is where to undo it.
It scanned a code but says it is not from this tool.
The codes here carry a marker and a piece number so that scanning an unrelated QR code cannot half-fill a message. Point it at the code this page is showing rather than at a poster or a payment code.
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