Password Strength Checker
Estimates password strength using entropy = length × log₂(character pool size), then penalizes for common patterns: dictionary words, keyboard sequences (qwer, asdf), repeated characters. Reports crack time across three threat models — online throttled (100 guesses/sec), offline slow hash like bcrypt (10k/sec), offline fast hash like SHA-256 (10B/sec). Password is never stored, transmitted, or logged.
Strength
Very weak
Length
0
Entropy
0.0 bits
Char pool
0
Password never leaves your browser. Entropy is an estimate — real attack difficulty depends on the hash function, hardware, and threat model.
How to use
- Type or paste a password.
- Read the strength bar and entropy.
- Check crack time at each threat level. Anything > 1 year on the 'offline fast' column is solid against most realistic attacks.
Frequently asked questions
- Is this safe to use with my real password?
- It runs entirely in your browser — no network calls, nothing stored. That said, type into random web tools at your discretion. If you'd rather not, test a similar-shape dummy password (same length, same character classes) instead.
- What's entropy?
- A measure of how many possible passwords could have produced this one, in bits. 60 bits = 2⁶⁰ ≈ 10¹⁸ guesses needed on average — strong against offline brute force. 30 bits ≈ 10⁹ guesses — cracked in seconds offline.
- Why does my password score lower than I expected?
- Length matters more than character diversity. 'Tr0ub4dor&3' (XKCD 936) is shorter and looks complex but has ~28 bits. 'correct horse battery staple' is plain words but has ~44 bits because it's longer.
- What about zxcvbn?
- zxcvbn is more sophisticated — it knows about leetspeak, dates, names, and L33t patterns. This calculator uses a simpler model. For production use cases (a signup form), prefer the actual zxcvbn library.
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