Nilanjan De focused on enhancing code quality, security, and maintainability across multiple 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, leveraging Go and Python. Nilanjan also improved code readability and consistency by correcting typos and standardizing naming conventions in projects such as safedep/vet and google/A2A, facilitating easier onboarding and reducing maintenance overhead. His work emphasized robust documentation, thorough testing, and secure database management, resulting in safer deployments and more reliable production systems.