What is a QR Code?

A grid of black and white squares that a phone camera reads from any angle, invented by a Toyota subsidiary in 1994 to track car parts. The three big squares in the corners are what a scanner finds first; they tell it where the code is and which way up. Up to thirty percent of the rest can be torn, smudged or covered and the code still reads, because the data is stored with enough redundancy to rebuild the missing part.

What it holds

Any text: a link, a phone number, a wifi network, a whole contact card. The ceiling is about 2,950 bytes, but that is a theoretical one - a code that big is a dense thicket of tiny squares that a phone struggles to focus on. A URL of fifty or sixty characters makes a code anyone can scan from across a room, which is what most of them are for.

Making a lot of them

Drop a .txt or .csv on this page and every line becomes its own QR Code, all of them zipped together. A CSV is read from its first column. Nothing is uploaded - the codes are drawn in this page, on your machine - so a list of five thousand costs nothing and takes as long as your laptop takes.