Have you thought about supporting a NIST mode to have it follow the NIST Federal Password Guidelines (Section 5.1)? This seems to be pretty standard in areas that I’ve worked as the password requirements. In general it just has a minimum length of 8, a minimum maximum length of 64, any ASCII printable character must be allowed and any unicode character ‘should’ be allowed, pasting should be allowed, a blacklist of compromised values is allowed and it is allowed to block often-guessed patterns such as dictionary words and so forth, more importantly it has this sentence: No other complexity requirements for memorized secrets SHOULD be imposed.

A library that verifies according to the NIST standards with a lot of configureable optional sets would be very nice.

Thanks, that seems like a reasonable consideration. Perhaps it could be implemented kind of like a preset. I added an issue to track it: Support NIST 5.1 requirements · Issue #4 · axelson/password-validator · GitHub