How the estimate works
Guessing tools do not try every combination in order. They start with leaked passwords, dictionary words, keyboard runs like qwerty, repeated characters and years. This checker looks for those patterns first and only counts the randomness that is left, then converts it to a time assuming 10 billion guesses a second.
It is a rough guide. Real speeds depend heavily on how a website stored your password, and a strong-looking password that has already leaked is weak no matter how it scores.
Is it safe to type a real password here?
The check runs entirely in this page and nothing is sent. Even so, the safest habit is to never type a real password into a website other than the one it belongs to. Use the checker to learn what makes passwords strong, then let a generator make the real thing.