Estimate how strong a password is from its length and character variety: entropy in bits, a rough crack-time estimate and a checklist of good practices.
No. The check runs entirely in your browser — the password never leaves the page.
From entropy: password length times the log2 of the character-set size, then rated from very weak to very strong.
No. Entropy assumes a random password; a long but predictable phrase or a leaked password can still be weak in practice.