Shannon Entropy Explained: A Smarter Way to Measure Password Strength

Common password strength meters rely on basic rules like minimum length or special characters, but these are poor indicators of true security according to information theory. Shannon entropy, measured in bits, offers a more accurate assessment by calculating the unpredictability of a password based on its length and the size of its character pool. A simple JavaScript formula — multiplying password length by the log base-2 of the pool size — can compute this entropy entirely within a browser without sending data to any server. Higher entropy means exponentially more brute-force attempts are needed to crack a password, making it a useful metric for estimating real-world cracking resistance. A client-side tool demonstrating this approach is available at KandZ Tools, where all calculations run locally in the browser to protect user credentials.