Minimum password length for registration form For user registration, I have disabled "Require e-mail verification when a visitor creates an account." to allow user create their own password at the registration form. Now, I wonder how to limit the password characters to minimum 6? I have tested several times, it seems drupal doesn't restrict any password characters even user keys in just 3 characters.
You might be looking of Password policy module

Features
Current constraints include:

Complexity constraint

Digit constraint

Letter constraint Letter/Digit

constraint (Alphanumeric)

Length constraint

Uppercase constraint

Lowercase constraint Punctuation constraint

Delay constraint Username

constraint Digit placement constraint

History constraint (checks

hashed password against a collection of users previous hashed

passwords looking for recent duplicates)



Also checkout this Quick demo.