OTP urls are of the format otpauth://TYPE/LABEL?PARAMS.

• TYPE totp or htop
• LABEL Free text - something like site:account
• PARAMS the following params are possible:
  • secret [required] the secret in base32
  • issuer [recommended] similar to the LABEL
  • algorithm [GA ignores] algoritm for OTP generation - one of: SHA1 (default), SHA256, SHA512
  • digits [GA ignores] number of OTP digits to display; defaults to 6 and can go to 8
  • counter [required for hotp] set this to 0
  • period [GA ignores, totp-only] seconds OTP will be valid for; defaults to 30

This article has more on the various URI schemes out there. Everything here is generated in browser by this QR code library.