Nilanjan De focused on enhancing code quality, security, and maintainability across five repositories, including BerriAI/litellm and Shubhamsaboo/adk-python. He addressed critical backend issues by correcting Gemini model cost calculations and hardening spend management endpoints against SQL injection using parameterized queries and improved input validation, all implemented in Go and Python. Nilanjan also improved code readability by standardizing naming conventions and correcting typos in comments and documentation, which streamlined onboarding and reduced maintenance friction. His work included comprehensive testing and documentation updates, ensuring safer deployments and more accurate cost tracking while positioning the codebase for easier future development.