I'm just checking out hashco.ws for the first time and cannot make any comments about quality or service, but one thing I want to ask:
In your opinion, how does one capital letter in a password raise the security?
Honestly, switch that off. It doesnt make a real difference.
It does a lot.
For example: any way of increasing the size of the char set used to make passwords lowers the risk of successful brute force attacks.
you're right, but if you don't put any boundary on the password choice than the character dictionary is actually made by any character. instead, if you force the user to use a capital letter it means you're actually reducing the dictionary dimension for that character.
if N = all possible characters, there exists:
N^8 8-chars completely free password, and
26+N^7 8-chars passwords with one capital letter