Password Strength Checker
Test how strong a password is — entropy, crack-time estimates, and concrete suggestions. Runs entirely in your browser; your password never leaves your device.
About the Password Strength Checker
This tool estimates how strong a password is and shows concrete ways to improve it. It calculates entropy (a measure of unpredictability in bits), forecasts how long a brute-force attack would take at different speeds, and lists suggestions such as adding length or mixing character classes. The whole check runs locally — your password is never sent over the network.
What the numbers mean
- Entropy — Roughly
log2(charsetSize) × length. More bits means exponentially harder to guess. Below 40 bits is weak; 60+ is reasonable; 100+ is excellent. - Character set size — The number of possible symbols the password draws from. Lowercase letters = 26; adding uppercase, digits, and common symbols pushes it past 90.
- Crack time — How long an attacker would need to try every combination. "Online" assumes ~1,000 guesses/sec (a typical login limit); "offline" assumes ~10 billion guesses/sec (a fast GPU hash rig).
How to use it
- Type a password into the box. The meter updates as you type.
- Click Show to reveal the characters while you type.
- Read the entropy, crack-time estimates, and suggestion list.
- Adjust the password until the meter is green and the suggestions clear.
Frequently asked questions
Is my password uploaded anywhere? No. Every calculation happens in JavaScript on your device. Nothing is sent to a server or stored.
Why does a long common word score low? Length alone isn't enough — if the password is a dictionary word or follows a common pattern, an attacker's dictionary attack will find it quickly regardless of length. Entropy rewards unpredictability.
Are these crack times accurate? They're estimates based on assumptions about attack speed. Real attacks may be faster (specialized hardware, leaked hashes) or slower (rate limits, lockouts). Treat them as a rough guide, not a guarantee.
What makes a strong password? Length is the single biggest factor. Aim for 16+ characters drawn from a mix of lowercase, uppercase, digits, and symbols — or use a passphrase of 4–5 random words. A password manager is the easiest way to get there.