Password Breach Checker

A password breach check tells you if your password has appeared in known data breaches. When companies are hacked, password databases often leak. Attackers use these lists for credential stuffing — trying the same password across many sites. Checking your password against breach databases helps you know if you need to change it.

K-anonymity is a privacy technique that lets you query a database without revealing your full secret. For passwords: you hash locally, send only a prefix of the hash, and the server returns all matching hashes. You check locally if yours is in the list. The server cannot infer your password or full hash from the prefix alone.

A strong password combines length (12+ characters), mixed case, numbers, and symbols. Avoid dictionary words and personal info. Use a unique password per site. Password managers generate and store strong passwords so you don't have to remember them.