Parth Kothari enhanced backend robustness and reusability across the googleapis/java-genai and google/adk-java repositories using Java and unit testing. He made the HttpApiClient base API public in java-genai, annotating it to clarify internal usage and prevent misuse, thereby enabling broader integration scenarios. In adk-java, Parth refactored the Vertex AI runner, introducing session encoding and decoding utilities, a default constructor, and improved error handling for session state and event parsing, which strengthened the reliability of Vertex AI integrations. He also developed targeted agent configuration tests to enforce correct agent setup, demonstrating a methodical approach to API and agent development.