Generator/Alternatives
Every authenticator computes the same six digits from the same secret — that part is a published standard, not a feature anyone owns. What differs is where the key lives, what happens when the phone does not, and what you can reach from a keyboard.
That Gen2FA replaces an authenticator app. It does not, and a comparison page claiming otherwise would be selling you something. An app is a vault: it keeps keys across reboots, restores them to a new phone, and keeps them off the machine you browse on. This site holds nothing you have not pasted in, and anything you save here is stored in readable form in one browser on one device.
The honest claim is narrower. A browser generator is the tool that works when the app is not in your hand — the phone is flat, lost, at home, or in a drawer while you are at a keyboard — and the tool that lets you check a setup key before you trust it.
All of them implement TOTP as specified in RFC 6238: the shared secret and the current 30-second time step run through HMAC, truncated to six digits. Because the standard is public, a code from one correct implementation matches a code from any other holding the same key. Nothing registers a device with the service, which is why you can enroll a phone app and still read the same code here.
When two authenticators disagree, the key is almost never at fault. A device clock out by more than about thirty seconds produces codes the service rejects — see why a code gets rejected.
If you already know which account you are trying to reach, the setup guides name where each service hides the text key behind its QR code, and which algorithm it issues. Getting that second part wrong produces codes that never work.