2FA Code Generator

Yes. It is completely free, with no sign-up, no watermark, and no usage limits.

No. Generation runs locally in your browser, so nothing is uploaded, logged, or stored.

Into this one, yes, and the reason is checkable: the code is computed in your own browser with the Web Crypto API, so the key never leaves the tab, is never sent to a server, and is not stored anywhere. Open your network tab and you will see no request carrying it. Be careful with other sites, though. A 2FA secret is a permanent credential, and any tool that sends it to a server has been handed your second factor for good.

Your password is fixed until you change it. A 2FA code is derived from a shared secret plus the current time, so it changes every 30 seconds and a stolen one is worthless a minute later. That is why two-factor authentication survives a leaked password.

When a service sets up two-factor authentication it shows a QR code plus a line of letters and digits, often labelled "manual entry", "setup key" or "can't scan the code". That line is the secret. You can paste it here with or without spaces, or paste the whole otpauth:// link the QR encodes and the digits, period and algorithm fill in themselves.

Nearly always the clock. Codes are derived from the current time, so a device running a few minutes off produces valid-looking codes for the wrong moment. Check that your system clock is set automatically. After that, confirm the digit count and period match what the service expects, most use 6 digits over 30 seconds.

No, and it is not meant to. Use it to get into an account when your phone is not to hand, to check that a secret you just saved actually works before you rely on it, or to test 2FA while building something. For everyday use, an authenticator app on a device you carry keeps the secret off your desktop.