An ASP.NET Web API developer designs, develops, and maintains HTTP-based services using the .NET framework. They create RESTful APIs for client-server communication, ensuring efficient data transfer between multiple platforms like web, mobile, and desktop. They are responsible for designing secure, scalable solutions, often involving data serialization, request routing, and error handling. They also integrate these APIs with other systems using various authentication methods. They handle testing, debugging, and improving the performance of these APIs. Additionally, they collaborate with front-end developers to align server-side logic with user-facing elements.