WiFi QR code generator

What a WiFi QR code actually contains

There is no image format for "wifi." What the code holds is a short line of text in a specific shape, and phone cameras have been taught to recognise it and offer a join prompt. A code for an open network called Cafe Guest holds exactly this: WIFI:T:nopass;S:Cafe Guest;;. Add WPA security and a password and it becomes WIFI:T:WPA;S:Cafe Guest;P:coffee12;;.

That format is worth understanding for one reason: it is a convention, not an international standard. It came out of ZXing, the open source barcode library, and phone makers implemented it because everyone else had. That is why support is broadly excellent but not guaranteed, and why a very old or unusual device may scan the code and show you the raw text instead of offering to join. Nothing is wrong with the code when that happens.

The T: field carries the security type. This tool writes WPA for a secured network, which is what current phones expect for WPA2 and WPA3 personal networks alike, and nopass for an open one. Ticking "hidden network" adds H:true;, which matters because a phone cannot discover a hidden SSID by scanning the air and has to be told the name explicitly.

The characters that quietly break a WiFi code

Semicolons end fields in this format and colons separate a key from its value, so a password containing either one would cut the join string in half and produce a code that scans but fails to connect. The format handles this by escaping five reserved characters with a backslash, and this tool escapes all five, in the browser widget and in the API behind it alike. The table below shows exactly what gets written.

This is worth checking if you generated a WiFi code elsewhere and it will not connect despite the password being correct. Take a password with a semicolon or a comma in it, encode it, and read the decoded string back with a QR code decoder. If the backslashes are missing, that is your bug.

How big to print it

WiFi codes stay small, which is good news. Measured at error correction level H, the level this tool uses, an open network with a short name is a version 4 code at 33 modules across. A WPA network with a 20-character password comes to version 7, 45 modules. Even a maximum-length 63-character WPA passphrase only reaches version 10 at 57 modules, and marking the network hidden adds one version step.

In practice that means a WiFi code on a table tent or a card works at a couple of centimetres square, far smaller than a full contact card needs. If you are putting one on a wall for people to scan from across a room, run the distance through our size calculator instead of guessing.

The one thing this cannot do

You cannot change the password without reprinting. The credentials are inside the pattern, so rotating a guest password invalidates every printed card at once. There is no version of a WiFi QR code that avoids this, ours included, because the phone has to read the credentials out of the image with no network available to look anything up.

If you rotate a guest password often, the usual workaround is to stop encoding credentials and encode a TangoQR link to a page that shows the current password instead. It costs your guests a tap and needs mobile data to load, so it is a real trade rather than a free win, but the printed card survives the rotation.