Designed to alert you whenever you login into an account, Google Password Checkup, checks whether your user and password have been involved in a security data breach known to Google.
It is recommended that an unsafe password should be changed if a security risk is found by Google, otherwise an account takeover could occur. Google Password Checkup also assesses password strength on the fly and whether it is strong or complex enough.
Since privacy is a concern of virtually everyone, Google maintains that your privacy is very important and critical. Although helpful data that is necessary to understanding data breaches is reported:
“We do report anonymous information about the number of look-ups that surface an unsafe credential, whether an alert leads to a password change, and the domain involved for improving site coverage.”
The checkup is essentially private by design and you are the only one who knows whether your account is unsafe. A similar tool is available for the Mozilla Firefox browser.