Shannon Entropy Password Checker

Summary

Type a password to instantly see its Shannon entropy in bits and a full character-set breakdown.

How it works

1. Type or paste your password into the input field.
2. The tool detects which character sets are present: lowercase, uppercase, digits, and symbols.
3. Pool size is calculated as the sum of characters in all detected sets.
4. Pool-based entropy = password length × log₂(pool size).
5. Frequency-based entropy = −∑ p(c) × log₂(p(c)) × length, where p(c) is the proportion of each unique character.
6. A strength label (Weak / Fair / Good / Strong / Very Strong) is assigned based on total bits.

Use cases

• Evaluate how strong a password is before using it on an important account.
• Compare multiple candidate passwords and pick the highest-entropy option.
• Understand why adding a symbol or digit meaningfully increases entropy.
• Teach information-theory concepts with a live, interactive example.
• Audit existing passwords stored in a password manager without sending them anywhere.
• Demonstrate why short passwords are weak even when they look complex.

Frequently Asked Questions