Password Strength Checker — Test Your Password Security

Password strength tools typically evaluate several criteria: length (longer is always stronger), character set diversity (uppercase, lowercase, digits, and symbols each expand the search space), absence of common patterns (keyboard walks like "qwerty", repeated characters, date formats, and sequential numbers), and absence from known breach lists (databases of billions of real passwords extracted from data breaches). Entropy, measured in bits, formalizes these factors into a single number: a password with N bits of entropy has 2^N possible combinations. A score of 40–60 bits is considered weak to moderate by current standards. 60–80 bits is strong. Above 80 bits is very strong and beyond the reach of any foreseeable computational attack. This tool estimates entropy based on the character pool implied by the characters actually present in the password and the password length, then applies pattern penalties when common sequences are detected.

Understanding how passwords are attacked helps you appreciate what strength ratings actually protect against. Brute-force attacks try every possible combination within a character set — the slowest method but guaranteed to eventually succeed, making entropy directly relevant. Dictionary attacks try known words, names, and phrases first, exploiting the fact that most human-chosen passwords are based on natural language. Hybrid attacks combine dictionary words with common substitutions and appended numbers or symbols. Credential stuffing takes username-password pairs from one leaked database and automatically tests them against other services. Rule-based attacks apply transformation rules to known words to generate millions of variants per second. Modern GPU-based cracking rigs can test billions of password candidates per second against stolen password hashes, making truly random passwords essential for any account you care about.

NIST Special Publication 800-63B is the most authoritative source of password guidance for US government systems, widely adopted by the private sector as well. Its key findings contradict much of the older complexity rules advice. NIST now explicitly discourages mandatory complexity rules such as requiring uppercase, numbers, and symbols, because they lead to predictable patterns without improving security meaningfully. Instead, NIST recommends prioritizing length — allowing passphrases of up to 64 characters — and screening passwords against lists of known compromised credentials. NIST also opposes mandatory periodic password changes unless there is evidence of compromise, because forced rotation leads users to make incremental, predictable changes. The most effective security measure besides length is using a unique password for every account, so that a breach of one service cannot be leveraged against others.

Even the strongest password provides only one factor of authentication — something you know. Multi-factor authentication (MFA) adds a second factor: something you have (a phone with an authenticator app, a hardware security key) or something you are (a fingerprint or face scan). With MFA enabled, an attacker who obtains your password still cannot access your account without the second factor. This dramatically reduces the practical risk of password compromise. Authenticator apps like Google Authenticator, Authy, or 1Password generate time-based one-time passwords (TOTP) that expire every 30 seconds. Hardware keys like YubiKey provide the strongest protection and are phishing-resistant. SMS-based MFA is better than no MFA but is vulnerable to SIM-swap attacks and should be avoided for high-value accounts. Always enable MFA on email, banking, and identity provider accounts — these are the accounts attackers prioritize most.

The single most impactful improvement most people can make to their password security is adopting a password manager. Password managers generate and store unique, randomly generated passwords for every account, removing the human tendency to reuse or weakly vary passwords across sites. They encrypt your credential vault with a master password and synchronize across devices. Popular options include Bitwarden (open-source, free tier), 1Password, Dashlane, and the native managers built into iOS and macOS. The master password should be a memorable passphrase — a sequence of random words — since it is the one credential you must type from memory. Enable biometric unlock (fingerprint or face) on mobile devices for convenience without compromising security. Review your password manager's breach alerts regularly and update passwords for any accounts flagged as compromised in known data breaches.