Worked on the openai-dotnet repository to deliver a custom serializer for message creation attachments, focusing on robust handling of tool definitions within the API. The solution filtered out 'file_search' tool definitions and ensured null-safety for tool lists, preventing serialization errors during message creation. Using C# and leveraging skills in JSON handling and serialization, the implementation introduced targeted unit tests to validate attachments with both file search and code interpreter tool types. This work addressed a specific issue in the codebase, enhancing the reliability and maintainability of the message creation process while improving test coverage for future development and integration.