[bsimpson]

I believe there's an algorithm to determine if a card number is valid (before determining if the other credentials are correct). Implementing that would probably be the most useful thing you could do in Skeuocard, as it helps people find typos in an otherwise inscrutable list of numbers.

[nwh]

It's called the Luhn algorithm, and no, the site doesn't seem to use it.

https://en.wikipedia.org/wiki/Luhn_algorithm

[roryokane]

It already does that. The credit card number has a red outline (box-shadow) if it is invalid. At least it did for me with the number 4555555555555555.