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Free Online Password Strength Checker

Check how strong your password really is: entropy, character variety, common-password detection and realistic crack-time estimates, computed entirely in your browser.

This tool runs entirely in your browser. Your password is never sent to a server, stored, or logged — not even temporarily.

Password Strength

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Security Checklist

  • At least 8 characters
  • At least 12 characters (recommended)
  • Contains an uppercase letter
  • Contains a lowercase letter
  • Contains a number
  • Contains a symbol (e.g. ! @ # $)
  • Not a commonly leaked password
  • No repeated or sequential pattern

Estimated Time to Crack

Entropy: —
Online attack, rate-limited (100/hour) —
Online attack, no rate limit (10/sec) —
Offline attack, slow hash (bcrypt, 10k/sec) —
Offline attack, fast hash + GPU rig (10B/sec) —

Why Password Strength Matters

Most account breaches do not come from sophisticated hacking — they come from weak, reused, or predictable passwords. Attackers run automated tools that try billions of combinations per second, starting with known leaked passwords and common patterns before moving to brute force. A password strength checker like this one estimates how long a real attack would take against your password, so you can fix weak spots before an attacker finds them, rather than after. It pairs well with a password generator when you need a brand-new, high-entropy password instead of testing an existing one.

How This Checker Calculates Strength

Strength is measured using entropy, expressed in bits — the number of guesses, as a power of two, an attacker would need to try every possible combination. Entropy depends on two things: the length of the password and the size of the character pool it draws from. Each character class you use expands that pool, which is why mixing types matters more than most people expect:

Lowercase letters (a–z) add 26 possible characters per position.

Uppercase letters (A–Z) add another 26 possible characters per position.

Digits (0–9) add 10 possible characters per position.

Symbols (!@#$…) add roughly 33 possible characters per position.

How to Create a Strong Password

Prioritize length over complexity — a 16-character passphrase is usually stronger and easier to remember than an 8-character jumble of symbols.
Mix at least three character classes (uppercase, lowercase, digits, symbols) to maximize entropy per character.
Never reuse the same password across sites; if one service is breached, reused passwords let attackers into every other account.
Avoid personal information (names, birthdays, pet names) and dictionary words, which are the first things password-cracking tools try.
Use a password manager to generate and store unique passwords for every account — try our own password generator for a quick, strong password.

Frequently Asked Questions

Yes. This checker runs entirely as JavaScript in your browser — your password never leaves your device, is never sent over the network, and is never stored or logged anywhere. You can verify this yourself: disconnect from the internet after the page loads, and the tool keeps working exactly the same, because no server call is ever made.

Entropy measures unpredictability in bits. Each extra bit doubles the number of guesses an attacker needs on average to find your password by brute force. A password with 40 bits of entropy requires about a trillion guesses on average; one with 80 bits requires roughly a trillion trillion. It is a mathematical estimate of worst-case guessing difficulty, not a guarantee against every possible attack.

Entropy grows with length much faster than with character variety. A 20-character lowercase passphrase like "correcthorsebattery" can have more entropy than an 8-character password packed with symbols, while also being easier for a human to remember and type. Length is the single biggest lever you control.

Length alone is not enough if the password is a known leaked password, a keyboard pattern, or a repeated/sequential sequence (like "abcdefgh" or "11111111"). Attackers try these patterns before brute force, so this checker penalizes them regardless of raw length — the checklist above shows exactly which check failed.

They are order-of-magnitude estimates based on published guessing speeds for different attack scenarios — a rate-limited login form versus an offline GPU cracking rig against a stolen, fast-hashed password database. Real-world results vary with the target system's defenses (rate limiting, hashing algorithm, salting), but the relative comparison between a weak and a strong password remains a reliable guide.