What makes a password strong?
Length matters most. Each extra character multiplies the number of guesses an attacker needs. A random 16-character password using letters, digits and symbols has more than 100 bits of entropy — far beyond what anyone can brute-force.
Is it safe to generate passwords online?
Here, yes: passwords are created on your device with crypto.getRandomValues, the browser's cryptographically secure random generator, and are never sent anywhere. Store them in a password manager rather than reusing them.