How the password strength score works
The score is an estimate based on length, character variety, repeated characters, and common risky patterns. It is useful for guidance, but no browser tool can guarantee that a password is impossible to crack. The safest approach is to use long, random, unique passwords and store them in a password manager.
A password can look complex and still be weak if it is based on a dictionary word, a name, a date, or a common phrase. A password can also be easier to use and safer when it is longer and random.