Analyze Your Password
Password analysis
What Is Password Entropy?
Password entropy is a way of describing the uncertainty involved in guessing a password. It is commonly expressed in bits. A higher theoretical entropy value represents a larger possible search space when the password is generated uniformly at random from a known set of characters.
For example, a randomly generated password selected from a larger character set has more possible combinations than a password of the same length selected from a smaller character set.
The theoretical entropy formula
If a password is generated uniformly at random from an alphabet containing N possible characters, and the password has L independently selected characters, the theoretical entropy is:
- H = theoretical entropy in bits.
- L = password length.
- N = number of possible characters in the alphabet.
This formula describes a random-generation model. It should not be interpreted as an accurate measurement of every password chosen by a person.
How Does This Calculator Work?
- Enter a password or passphrase in the input field.
- The calculator counts its characters and detects the character categories used.
- It estimates the theoretical search space from the detected character pool and password length.
- It checks for simple patterns such as repeated characters, sequential characters, and predictable words.
- It displays an indicative strength category and practical feedback.
The tool runs in your browser using JavaScript. The password is not submitted to a PHP endpoint, saved in a database, or sent to a third-party password analysis service by this calculator.
Why Entropy Is Not the Whole Story
A password can contain uppercase letters, lowercase letters, digits, and symbols and still be predictable. For example, adding a single symbol to a common word does not necessarily make it difficult to guess.
Passwords chosen by people are not usually selected uniformly at random. They may contain names, dates, dictionary words, keyboard patterns, familiar substitutions, or repeated characters. A simple character-pool formula cannot reliably capture all these patterns.
This is why the calculator provides pattern warnings in addition to its mathematical estimate. It does not claim to perform a complete dictionary attack simulation or check passwords against a database of breached credentials.
Tips for Creating Strong Passwords
- Prefer long, unique passwords or passphrases.
- Use a password manager to create and store unique passwords.
- Avoid reusing the same password across different websites.
- Avoid personal information, predictable phrases, and common patterns.
- Enable multi-factor authentication when available.
- Use a breached-password blocklist when implementing password creation on your own application.
Current NIST digital identity guidance emphasizes password length, supports long passphrases, and discourages rigid character-composition rules. A long, unique password is generally more useful than simply satisfying a checklist of character types.
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