Password Strength Checker

What this tool does

Password Strength Checker goes beyond naive "length + symbol" scoring by detecting common passwords, dictionary words (including leetspeak substitutions), sequences, repeated characters, keyboard walks and dates, computing a realistic entropy estimate from the cheapest combination of patterns an attacker would actually try, with crack-time estimates for four real-world attack scenarios.

A naive strength meter that just counts length and character types gets fooled constantly, "Password1!" scores well on that basis despite being one of the first guesses any real attacker tries, because it’s a known common password with predictable capitalisation and punctuation.

This checker instead looks for the actual patterns attackers exploit, common password lists, dictionary words (including leetspeak substitutions like 4 for a or 3 for e), sequences like "abcd", keyboard walks like "qwerty", repeated characters and dates, then computes entropy from the cheapest combination of patterns covering the whole password, which is how real cracking tools actually approach guessing.

How to use Password Strength Checker

1. Type (or paste) a password into the field.
2. Review the Score and Estimated entropy.
3. Check Patterns found for anything detected as risky.
4. Read the feedback for specific suggestions to improve it.

Tips for better results

• The "Estimated entropy" (after pattern analysis) is the realistic figure, it’s always less than or equal to the naive "Brute-force entropy" (length × log2(pool)), since it accounts for predictable patterns a real attacker would try first.
• A password built from several unrelated random words (a passphrase) typically scores far better here than a shorter password with substituted symbols, since swapping "e" for "3" is a well-known trick already baked into cracking dictionaries.
• Nothing you type here is sent anywhere; checking runs entirely in your browser, so it’s safe to test your actual passwords, not just examples.
• Nearby, repeated, or sequential characters ("aaaa", "1234", "qwerty") each add very little real entropy even though they visually look like "more characters"; the pattern detector catches and discounts these specifically.

Common use cases

• Checking whether a password you already use is actually strong, or just looks strong.
• Understanding specifically which pattern (common word, sequence, keyboard walk, date) is weakening a password.
• Comparing a hand-picked password against a tool-generated one to see the real entropy difference.
• Teaching or demonstrating why naive length-and-symbol scoring is misleading.

Common mistakes to avoid

• Trusting a simplistic strength meter elsewhere that only checks length and character variety; those meters routinely rate genuinely weak, pattern-based passwords as "strong".
• Assuming leetspeak substitutions (4 for a, 3 for e, 0 for o) meaningfully strengthen a password; they’re well known and already incorporated into every serious password-cracking tool’s dictionary.
• Reusing a password that scores well here across multiple accounts; strength and uniqueness are two separate, equally important properties.