Google2FA is a standalone PHP library implementing the Time-based One-Time Password (TOTP) algorithm as specified in RFC 6238, fully compatible with Google Authenticator and similar authenticator apps. It provides secure secret key generation (base32-encoded), HMAC-based OTP computation with configurable algorithms (SHA1, SHA256, SHA512), and OTP verification with a sliding window to accommodate clock drift. The library also includes a helper for generating otpauth:// URLs for QR code integration. It has zero external runtime dependencies beyond a constant-time base32 encoder and is designed as a single-class library with traits for modularity. The codebase is well-tested across PHP 7.4 to 8.6 (beta), employs static analysis (PHPStan, Psalm), and follows a clean, maintainable architecture with clear exception hierarchies. It is not a framework but can be used in any PHP project.