> Alphanumeric data, in the context of QR codes, comes from the following alphabet of 44 characters:

> 0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ $%*+-.:

This is wrong: alphanumeric has 45 characters, not 44. It’s missing the second last character, /.

(The slash is important because it makes alphanumeric-mode URLs possible: you can write HTTPS://EXAMPLE.COM/PATH which will be parsed to https://example.com/PATH. No query string or fragment due to no ?&=#, and your server must accept the uppercase path, either serving it or redirecting to the lowercase and then serving that.)

An alphabet size of 45 is the largest that will fit into 5½ bits per character (log₂ 45 ≈ 5.49).