TOTP Generator

The code is HOTP from RFC 4226 applied to T = floor(Unix time / period), as defined in RFC 6238 §4. HMAC runs in the browser (Web Crypto).

Examples You Can Reproduce

Each example uses a published test secret, so you can check the output against the RFC or another library.

RFC 6238, SHA-1. Secret GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ (the ASCII string 12345678901234567890 in Base32), 8 digits, Unix time 59:

94287082 is the first row of the table in RFC 6238 Appendix B. The previous code is the time step T = 0; its last six digits, 755224, are the count-0 value in RFC 4226 Appendix D.

RFC 6238, SHA-256. Choose SHA-256 and use the 32-byte seed from the RFC’s reference code: GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQGEZA====. At Unix time 1111111109 the code is 68084774, and the next code, 67062674, is the RFC row for 1111111111, which falls in the next step. The RFC prose names only the 20-byte seed, but its Appendix A code uses 32- and 64-byte seeds for SHA-256 and SHA-512, and the published values only match those. The trailing ==== is accepted; the URI leaves it out.

Cross-check with pyotp. pyotp 2.10.0 gives the same values:

import pyotp
pyotp.TOTP('GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ', digits=8).at(59)   # '94287082'
pyotp.TOTP('JBSWY3DPEHPK3PXP').provisioning_uri(name='alice@google.com', issuer_name='Example')
# 'otpauth://totp/Example:alice%40google.com?secret=JBSWY3DPEHPK3PXP&issuer=Example'

Type Example and alice@google.com into Issuer and Account with secret JBSWY3DPEHPK3PXP and the tool builds the same URI. At Unix time 1234567890 that secret gives 742275. It also shows a warning: the key is 80 bits, below the 128 bits that RFC 4226 §4 requires. The secret comes from Google’s Key Uri Format page.

Input errors. GEZDGNBV1Y3TQOJQ is refused because 1 is not in the Base32 alphabet (RFC 4648 §6). The digits 0, 1, 8 and 9 never occur, so they usually mean O, I, B or g was misread. GEZDGNBVG is refused because no Base32 string has 9 characters: a group of 8 cannot end after 1, 3 or 6 characters. pyotp rejects both too (Non-base32 digit found, Incorrect padding).

Checking a Key You Typed by Hand

When a phone cannot scan the QR code, setup pages show the secret as text. Type one character wrong and the app shows codes the server never accepts, with no hint why. Paste the same text here. If the code differs from the app’s code in the same 30 seconds, one of the two copies is wrong. If they match but the service rejects them, check the clock.

Clock errors are common because TOTP depends on both sides agreeing on the time. RFC 6238 §5.2 recommends that a verifier accept at most one step of network delay, and §6 describes a configurable window of steps for drift. pyotp’s verify() has valid_window=0 by default, so a server built on it accepts only the current step. The tool compares your clock with the server’s Date header once, and warns if the difference is more than about 3 seconds beyond the measurement error.

How It Differs from Other Online TOTP Generators

We tested four generators that rank for “totp generator” or “2FA” on 2026-09-30, with the same inputs:

• Invalid characters. With GEZDGNBV1Y3TQOJQ, totp.danhersam.com showed a code (708688), BrowserScan’s 2FA tool showed a code (its red “invalid key characters” line was also there for the valid RFC secret), and 2fa.cn returned a code. Token2’s TOTP Toolset converted it to a different hex seed without a message. Here it is an error that names the character.
• Where the secret goes. BrowserScan writes the key into the address bar (/2fa#GEZD…), so it ends up in browser history, and its page suggests putting the key in the URL path. 2fa.cn requested https://2fa.cn/codes/<secret>, so the code was computed on its server. Authgear’s page says it saves up to 10 secrets in the browser. This tool keeps the secret in the page’s memory only.
• Settings. danhersam has no algorithm choice. Token2’s page is SHA-1 only (SHA-256 is a separate page) with periods of 30 or 60 seconds. Here SHA-1, SHA-256 and SHA-512 and any period from 1 to 86400 seconds are available, plus a fixed Unix time for test vectors.
• otpauth:// input. BrowserScan showed no code for a pasted otpauth:// URI. Here the URI fills in all fields.

Token2 shows several codes around the current time, which is useful for drift checks; this tool shows one step on each side.

Limits

• TOTP only. otpauth://hotp/ URIs are refused, and there is no counter mode.
• Digits and algorithms. 6 or 8 digits, as in the Key Uri Format. SHA-1, SHA-256 and SHA-512. The period is a whole number from 1 to 86400 seconds, counted from the Unix epoch (T0 = 0).
• App support. The Key Uri Format page says Google Authenticator ignores algorithm and period, and on Android also digits. The tool shows this warning under the QR code when you change any of them.
• No QR image input. Decode a screenshot with the QR Code Decoder, then paste the otpauth:// text here. To make a QR code for other text, use the QR Code Generator.
• Nothing is saved. Reloading the page clears the secret by design.
• Clock check. The server Date header has one-second resolution, so offsets under about 3 seconds are not reported. If the request fails, no warning appears.

To see the HMAC step on its own, try the HMAC Generator; for account passwords, use the Password Generator.