Password Strength Checker

See how strong a password really is. This estimates its entropy and rough time-to-crack, and tells you exactly how to improve it — all locally in your browser. Nothing is sent or stored.

Free vs paid — when to upgrade

What this free tool is great for: a quick, one-off job with no signup — it runs entirely in your browser, so nothing leaves your device and there's nothing to manage.

Its honest limit: it produces a one-off output — it won't store, track, brand or manage them at scale, and it can't tell you what happens after you share it.

Where Passpack does more: A strong password is only useful if you can store and share it safely. A zero-knowledge password manager like Passpack keeps your team's passwords in encrypted vaults — at a low per-user price.

Try Passpack →

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What "strong" actually means

Most people judge a password by how complicated it looks — and that instinct is exactly wrong. Strength isn't about looking cryptic; it's about how many guesses an attacker would need to find it, a quantity security people call entropy. A password that looks wild to you ("P@ssw0rd!") can sit near the top of every cracking list, while four random common words can be practically unguessable. This checker estimates that guess-resistance in your browser (nothing you type leaves your device) and, more importantly, shows you which property is doing the work — because once you understand what actually makes a password strong, you stop falling for the tricks that only make one look strong.

How checkers estimate strength

A naive meter counts character types: lowercase, uppercase, digit, symbol — tick the boxes, get a green bar. That's the standard most websites use, and it's why they'll happily accept "P@ssw0rd1" while rejecting a vastly stronger passphrase. A serious checker instead models how real attackers work: it looks for dictionary words, common substitutions (@ for a, 0 for o), keyboard walks (qwerty, asdf), dates, repeated patterns, and known-leaked passwords, then estimates how many guesses a cracking rig would need. The difference matters because attackers don't guess randomly — they guess in the exact order humans tend to choose, which is why human-invented passwords fall so much faster than the character-type checkboxes suggest.

The maths of guessing

Entropy grows exponentially with length, and that single fact should drive every password decision. Each extra character multiplies the search space by the size of the character set — so going from 8 to 16 characters doesn't double the work for an attacker; it multiplies it by a number with more than a dozen zeros. Meanwhile, adding a symbol to a short password barely moves the needle. Modern cracking hardware tries billions of guesses per second against stolen password databases, which sounds unbeatable — until you realise that a truly random 16-character password would still take longer than the age of the universe. Length times randomness wins; nothing else comes close.

Why "Winter2026!" fails every real test

The classic corporate password — capitalised word, year, exclamation mark — passes almost every website's complexity rules and fails almost instantly against a real attack. Cracking tools don't brute-force blindly; they run rule engines that take dictionary words and apply exactly these mutations: capitalise the first letter, append a year, append punctuation, swap letters for lookalike digits. Millions of leaked passwords trained these rules, so your "clever" pattern is literally in the attacker's playbook. This is the core insight a good checker makes visible: predictability, not character variety, is what kills passwords — and human brains are predictability machines.

Checking is safe here — but be picky elsewhere

A fair question: is it safe to type a password into a checking tool at all? Here, yes — this checker runs entirely in your browser; the password never leaves your machine, nothing is sent or stored. But the caution behind the question is healthy. Never type a real, in-use password into a random website you don't trust, because a malicious "checker" is a perfect harvesting tool. The safe pattern: test candidate passwords or patterns before you adopt them, use client-side tools (like this one), and if you want to know whether an existing password has appeared in breaches, use reputable breach-checking services that use privacy-preserving lookups rather than sending your password anywhere.

What to do with a weak result

If the meter comes back weak, resist the urge to patch the same password with one more symbol — that's rearranging deck chairs. The upgrade path is structural: make it longer (16+ characters), make it random (generated, not invented), and make it unique to that account. For passwords you must memorise, switch to a passphrase: four or five genuinely random words beat any mutation of a single word. And if you notice you're reusing a password across sites, that's the most urgent fix of all — a strong reused password is one breach away from being a weak one everywhere it's used.

Strength is only half the story

Here's the honest limit of any strength checker: it evaluates one password in isolation, but most real-world account takeovers don't involve guessing at all. Credential stuffing — replaying email-password pairs from one site's breach against every other site — defeats the strongest password if you reused it. Phishing captures your password at a fake login page regardless of its entropy. That's why the modern security stack is: unique random passwords everywhere (a manager's job), two-factor authentication on everything important (your safety net), and healthy suspicion of login links in emails. A 100/100 strength score on a reused password is a false comfort — uniqueness beats strength when the two conflict.

Rotating passwords: when it helps and when it hurts

Old corporate wisdom said to change every password every ninety days — and modern guidance has quietly reversed it. Forced frequent rotation makes humans choose weaker, patterned passwords (Summer2026 becomes Autumn2026) and write them down, which lowers security overall. Today's consensus: rotate a password when there's a reason — the service was breached, you may have typed it into something suspicious, someone who had access left — and otherwise let a strong, unique password live. The exception is shared credentials in a team, which deserve rotation whenever membership changes. Rotation is a response to events, not a calendar ritual; a checker plus a manager makes each rotation painless when it's genuinely needed.

From checking one password to managing them all — where Passpack does more

This checker answers "is this password any good?" — useful every time you create one. But the real-world problem is scale: dozens or hundreds of accounts, each needing a unique, strong password, some shared with colleagues, all needing to be available on every device. That's where a password manager like Passpack does more: it generates strong passwords by default, stores them encrypted, fills them automatically, and lets teams share credentials with proper permissions instead of pasting them into chat. Check your password here to learn what strong means; then let a manager make strong-and-unique the default for every account you own, because that — not one heroic password — is what actually keeps you safe.

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