This extension uses an export of passwords from Google Smart Lock (Chrome's password manager) and checks them against Pwned Passwords using the k-anonymity checker (i.e. it never sends your actual password, it sends a substring of a hashed version of your password).
You can get the Chrome Passwords.csv file by going to chrome://settings/passwords in Google Chrome,
then clicking the three dots to the right of the Saved Passwords header and downloading it somewhere.
bundle install
bundle exec ruby check-passwords.rb Chrome\ Passwords.csv
Will check each password line by line. If a password has been pwned over 10,000 times it'll be red, otherwise it's yellow. It's up to you to decide whether you'd accept the risk of using a password that's shown up in plain text in breaches once, 10 times, 100 times...