zxcvbn is a password strength estimator inspired by password crackers. Through pattern matching and conservative entropy calculations, it recognizes and weighs 10k common passwords, common names and surnames according to US census data, popular English words, and other common patterns like dates, repeats (aaa), sequences (abcd), keyboard patterns (qwertyuiop), and l33t speak.
Consider using zxcvbn as an algorithmic alternative to password policy — it is more secure, flexible, and usable when sites require a minimal complexity score in place of annoying rules like "passwords must contain three of {lower, upper, numbers, symbols}".