OTP Checker

The OTP Checker is a developer-oriented tool that validates one-time passwords (OTP) and time-based OTPs (TOTPs). It accepts a secret, digits, algorithm, and a time step to either generate an expected code or verify a provided code. This supports debugging of MFA flows and QA validation of 2FA integrations.
Conceptually, the tool implements the RFC 6238 (TOTP) and RFC 4226 (HOTP) algorithms by deriving a counter from time or a supplied value, computing an HMAC with the chosen digest, and applying dynamic truncation to produce a numeric code of the requested length. It can tolerate clock drift by evaluating neighboring counters when verification is performed.
Key users are security engineers, developers integrating 2FA, and QA teams that need deterministic OTP validation in tests or CI pipelines. It differentiates itself by offering both generation and verification paths, offline testing capability, and explicit handling of common edge cases like misconfigured secrets or mismatched algorithms.
Typical use cases include validating TOTPs from authenticator apps, testing HOTP-based tokens in legacy systems, and diagnosing errors in MFA setup without relying on live user sessions.