Measuring Password Strength with Shannon Entropy
Are your passwords actually secure, or do they just look complex? The Password Strength Checker above evaluates the cryptographic resilience of your passwords locally in your browser. Instead of arbitrarily guessing how "strong" a password is based on length alone, this utility calculates the mathematical Shannon Entropy to provide an objective score.
What is Shannon Entropy?
Introduced by Claude Shannon in 1948, Shannon Entropy measures the exact amount of uncertainty or unpredictability in a piece of information. In the context of cybersecurity, it calculates how many possible combinations an attacker would need to guess to break your password.
The entropy score is measured in bits. The formula evaluates the size of the character pool used (e.g., lowercase only = 26, uppercase + lowercase = 52, all symbols = 94) and exponentially scales it by the length of the string.
- < 35 bits: Very weak. A modern GPU array can crack this in seconds.
- 36 to 59 bits: Moderate. Safe against casual guessing but vulnerable to dedicated offline brute-force attacks.
- 60 to 79 bits: Strong. Safe against most modern cracking hardware.
- 80+ bits: Excellent. Mathematically unbreakable within a human lifetime using current technology.
Dictionary Words vs. Randomness
A password like Tr0ub4dor&3 might seem complex because it includes substitutions, but because it relies on a dictionary word, it is vulnerable to Dictionary Attacks. Hackers use massive databases of known words, leaked passwords, and common substitutions (like swapping 'o' with '0') to crack these instantly.
Conversely, a completely random string of characters (like k8#P9z$mQ2!w) has no linguistic roots, meaning an attacker must rely purely on guessing every possible combination (brute-force). This is why a random 12-character password is often stronger than a 16-character password made of common words.
Frequently Asked Questions (FAQ)
Is it safe to type my real password here?
Yes. The analyzer runs entirely via client-side JavaScript. Your keystrokes never leave your device, and no data is transmitted to our servers or stored in any database. However, as a general security rule, you should never type your actual master passwords into any third-party website unless strictly necessary.
Why do some sites require a special character?
Forcing a special character expands the "character pool" from 62 (letters and numbers) to 94. While this slightly increases the theoretical entropy, modern security standards (like NIST) now recommend focusing on overall length rather than forcing specific character types, as length provides a much larger mathematical advantage against brute-force attacks.