Password Strength Tester — Free & Private

About Password Strength Tester

This tool analyzes password strength using multiple factors: length, character variety, entropy (randomness), common pattern detection, and dictionary word checking. It estimates the time needed to crack the password using modern hardware.

Your password is analyzed entirely in your browser and is never sent to any server. For breach checking, only the first 5 characters of a hash are sent to the Have I Been Pwned API (k-anonymity), so your actual password is never exposed.

Password entropy measures randomness in bits. A truly random 12-character password using uppercase, lowercase, digits, and symbols has about 79 bits of entropy — enough to resist brute-force attacks for centuries with current hardware. However, patterns like 'Password123!' have far lower effective entropy because attackers try common patterns first.

Modern password attacks use dictionary lists, known breach databases, and rule-based mutations (appending numbers, replacing letters with symbols). The Have I Been Pwned database contains over 900 million compromised passwords. This tester checks your password against that database using k-anonymity — only the first 5 characters of the SHA-1 hash are sent, so your full password is never transmitted.

For maximum security, use a passphrase of 4-5 random words (e.g., 'correct horse battery staple') which is both strong and memorable, or generate a random password with the Password Generator and store it in a password manager. Avoid reusing passwords across sites — a breach on one site compromises all accounts sharing that password.