What Is OTP
OTP means One-Time Password. It is used to confirm an action or sign-in and should be valid only once or for a short time. In 2FA, an OTP becomes the second factor after the password.
A user can receive an OTP by SMS, email, push approval, hardware key, or authenticator app. App-based codes most often use TOTP, where the code depends on time.
OTP and TOTP
TOTP is a type of OTP. During setup, a service issues a secret through a QR code or Base32 token, and the generator calculates a one-time code from that secret and the current time. TOTP codes refresh regularly and do not require a server message for every new code.
SMS codes are easy for users, but they depend on carriers and can be intercepted. TOTP is usually stronger when the secret is stored safely.
When an OTP Generator Online Helps
An OTP generator online is useful when a code must be produced quickly from an existing TOTP secret: checking a test account, helping a user, or completing an internal operation. It does not replace security rules.
Protect the secret, store recovery codes, and do not publish the Base32 token in open places. The one-time code is meant to be typed into the target site; the secret that creates such codes must remain private.