Lately I have been working on developing a new product key system and realized that one of the core rules of the road is not documented anywhere I can find (which is crazy in this day and age when everything is supposed to have already been said).

The rule is pretty simple once you think of it. You should never include the numbers 0 or 1 or the letters L, O or I in a license key that you require users to ever type. The reason is that there is too much chance of confusion that will cause the key to fail. Zero looks like the letter “O”, lower case “L” looks like 1 and upper case “I” in many fonts.

A simple set of rules, but ignored way too often. The only exception and I think it should be used sparingly is when the key is all numberics since that should remove the ambiguity provided you clearly state that the key is all numeric.

Random ramblings perhaps, but it will save you down the road on customer support calls and that means money!