QR Code Generator

In theory a few thousand characters; in practice far less if you want it scanned. Every extra character adds modules to the grid, and a dense code needs either a larger print or a closer, steadier camera. This generator handles up to about 400 characters at error correction level M, which comfortably covers a web address, a wifi login or a short contact card, and refuses anything longer rather than producing a code that technically encodes your data but no phone can read. If you need to encode more, put the content on a page and encode the link to it.

A wifi QR code is just a short piece of formatted text — the network name, the security type and the password — that phones recognise and offer to connect with. It saves reading a 20-character password aloud across a café. The safety consideration is straightforward: anyone who can see the code can join the network, so print it for a guest room or a counter, and do not post it where it can be photographed from the street or published online. The password is encoded in plain text inside the code, which also means the image itself should be treated as the password.

Four reasons, in order of how often they happen. The quiet zone was cropped — a QR code needs a clear margin of about four modules on every side and cropping to the edge breaks it. The contrast was inverted or reduced: dark on light is what readers expect, and light-on-dark or a code over a photograph often fails. It was printed too small for the scanning distance — a rough rule is a code of at least a tenth of the distance it will be scanned from. Or a logo was pasted over the middle: error correction tolerates some damage, but level M only about 15 per cent, and a logo usually costs more than that.