Bcrypt
Hash a password at any cost factor, or check one against an existing hash.
Nothing you enter is sent anywhere. The engine downloads on first use.
Cost factor
Each step doubles the work. Cost 12 takes roughly a quarter second on a modern server, which is the point: it makes an attacker with a leaked database do the same work for every guess. Under 10 is too fast to be useful in 2026.
Runs in your browser, so a production hash pasted here is never transmitted. Bcrypt embeds its own salt, which is why the same password hashes differently every time and why you compare with the library rather than by string equality.