The tool in the browser is able to detect if a password has been compromised not only on Google - but other website as well.
However, they have reassured users that their data will not be shared.
Google's security team members Kurt Thomas and Adam Dawes, who created the extension, said: "We built Password Checkup so that no one, including Google, can learn your account details.
"To do this, we developed privacy-protecting techniques with the help of cryptography researchers at both Google and Stanford University."
The pair added that they will be tweaking the tool "in the coming months".
They continued: "This is our first version of the Password Checkup, and we'll be refining in the coming months."
Google are also working on their Cross Account Protection tool, which stops hackers from using Google Sign In details on third-party services.