Developed a feature flag evaluation SDK for the Automattic/wp-calypso repository, focusing on cross-runtime parity with an existing PHP implementation. The work introduced hash and bucket primitives using TypeScript, enabling consistent feature flag evaluation logic across environments. A robust evaluation pipeline was established, supporting ordered rule evaluation and a parity gate to ensure alignment with PHP behavior. The SDK incorporated key operators for condition matching, such as equality and logical operations, and enforced fail-closed behavior for unknown operators. Comprehensive test coverage and documentation were provided, with no new runtime dependencies added, reflecting a methodical approach to full stack development and testing.