Wee QR is a really simple QR Code generator on Rack.
Wee QR depends on on the qrencoder gem, which depends on libqrcode. Installation on OS X (using brew, bundler) looks something like this:
$ brew install qrencode
$ git clone git@github.com:kenkunz/wee-qr
$ cd wee-qr
[review and accept the .rvmrc]
$ bundle install
Run it with your rack server of choice. Go to the app’s url, with the content you want encoded in the query string. The response should be QR code png. You can optionally include a module size as a path parameter (default is 5).
For example, I’m running Wee QR at qr.dev, so http://qr.dev/foo returns a QR code that encodes “foo”, and http://qr.dev/10?bar%20baz returns a larger QR code (10 pixel modules) that encodes “bar baz”.