🔐 Privacy-Preserving Check

Has your password been breached?

Check any password against known data breaches. Your password is never sent anywhere — only a tiny, anonymized fragment of its hash is.

How this stays private: your password is hashed (SHA-1) right here in your browser. Only the first 5 characters of that hash are sent to Have I Been Pwned's Pwned Passwords API — a technique called k-anonymity. Thousands of different passwords share those same 5 characters, so the service never learns which password you actually typed, and the full password never leaves this page.

Powered by Have I Been Pwned, built the Flassword way

Real breach data, with the same privacy-first defaults as every other tool here.

k-Anonymity by design

Your password never leaves your device. Only a 5-character hash prefix is ever transmitted.

Real breach data

Checked against a database of hundreds of millions of passwords exposed in known breaches.

Nothing logged on our end

Flassword doesn't see or store your password either — the check happens entirely in your browser.

Frequently asked questions

Everything you might want to know about the breach checker.

No. Your password is hashed in your browser first. Only the first 5 characters of that hash — never the password, and never the full hash — are sent to check for a match. This technique is called k-anonymity, and it's explained in more detail above.

Have I Been Pwned is a widely trusted, independent breach-notification service run by security researcher Troy Hunt. Its Pwned Passwords database aggregates hundreds of millions of passwords exposed in known data breaches, and offers a free, privacy-preserving API specifically designed for checks like this one.

Stop using it immediately, on every account where it appears, and replace it with a new, unique, randomly generated password. If you reused it anywhere else, change it there too — see our guide on why you should never reuse passwords.

It means it hasn't turned up in a known, indexed breach yet — not that it's inherently strong. A short or predictable password can still be guessed even if it has never leaked. Pair this check with our Password Strength Checker for the full picture.

Checking against real breach data requires comparing against a database of known-exposed passwords that no browser can hold locally. Every other tool on Flassword works fully offline; this is the one exception, and it's built to leak as little information as technically possible while still doing that job.

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The same private, client-side approach for everything else you need to generate.