Password checker

What the instant strength estimate tells you

The strength panel runs entirely in your tab. It measures raw entropy, flags common structures like dictionary words, keyboard walks, repeated runs and simple substitutions that cracking dictionaries encode explicitly, and translates that into crack-time bands for offline and online attacker models. A four-word random passphrase regularly outranks an eight-character symbol soup precisely because each additional random word multiplies the search space by thousands while remaining typable.

That estimate is conservative by design: attackers do not try every combination naively, they prioritize human-chosen patterns. So a short complex string that matches a common template is correctly called weak even though its character set looks varied.

• Length dominates: each additional random character or word multiplies possibilities exponentially.
• Repetition and pattern collapse the space: 'aaaa', '1234', 'qwerty' and leetspeak swaps are pre-computed.
• Uniqueness matters more than brilliance: a strong password reused across accounts is strong everywhere until one leak makes it weak everywhere.

How the leak check uses k-anonymity

The leak database holds SHA-1 hashes of hundreds of millions of compromised passwords. Rather than sending your password, the page hashes it locally, transmits only the first five hex characters of that hash, and receives back all hash suffixes that share that prefix. Your browser completes the comparison locally and reports whether an exact match exists and how many times that password has been seen.

Only a small fragment leaves the device, and that fragment is shared with thousands of other users, making reversal infeasible. The approach, popularized by Have I Been Pwned's range API, means even a network observer cannot learn the candidate you tested beyond the coarse prefix.

Reading a result honestly

Strength and exposure are separate axes. A string can be structurally strong and still be compromised because someone else chose the same string and then leaked it, 'correct-horse-battery-staple' as a quoted example paradoxically became weak once it was printed in an article. Conversely, a structurally weak string that is not in the current corpus is still weak because the first offline brute force will find it.

If the leak check says your password has been seen, rotate it everywhere you used it, starting with email and banking. If it says it has not been seen, judge it by the strength estimate: length and randomness still decide whether it would survive the next database dump.

A practical migration path

No one should memorize 150 unique high-entropy secrets. Choose one strong master passphrase you can type reliably, provision a reputable password manager with it, and let the generator create per-site secrets you never need to recall. Replace reused or leaked passwords over two weeks rather than in a marathon, but start with the three that gate recovery: your primary email, your password manager, and your cloud backup.

Store printed recovery codes for those three offline. A vault that cannot be recovered after a lost device helps no one.