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README.md

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+# teotipi
+
+A Gleam CLI and library for generating TOTP codes (RFC 6238).
+
+## Usage
+
+```bash
+gleam run -- <base32-secret>
+```
+
+**Example:**
+
+```
+$ gleam run -- JBSWY3DPEHPK3PXP
+123456
+```
+
+The secret is your Base32-encoded TOTP key (the one you'd scan as a QR code in an authenticator app).
+
+## Library API
+
+```gleam
+import teotipi
+
+// Returns a zero-padded 6-digit string
+teotipi.totp_string("JBSWY3DPEHPK3PXP")  // Ok("123456")
+
+// Returns a raw integer
+teotipi.totp("JBSWY3DPEHPK3PXP")          // Ok(123456)
+```
+
+Both functions return `Error(Nil)` if the secret is not valid Base32.
+
+## How it works
+
+Implements TOTP as defined in [RFC 6238](https://datatracker.ietf.org/doc/html/rfc6238):
+
+1. Decode the Base32 secret
+2. Compute the time counter (`unix_seconds / 30`)
+3. Run HMAC-SHA1 over the 64-bit counter
+4. Apply dynamic truncation to extract a 6-digit code
+
+## Testing
+
+```bash
+gleam test
+```
+
+## License
+
+MIT — see [LICENSE](LICENSE).