The design process of an application programming interface (API) is crucial in ensuring that it produces the desired functionalities. The fundamental API design influences how well users can consume it and the general user experience. The design process combines a series of guidelines to meet initial expectations and continue to work consistently. API designers closely follow industry best practices, design patterns, and user needs to develop software that presents excellent functionality. REST is the most popular design style, but other architectural designs like GraphQL are also used. API design principles prioritize simplicity and flexibility, allowing users to access the platform with ease. The design process involves defining simplicity in data formats, method structure, authentication, and usage policies. It also requires considering the scope of operations and potential user space. Developers focus on business entities that the API exposes to develop a system that offers required functionalities. The design process asks vital questions such as whether the API supports use cases and whether it has a datacenter in target geographical locations. Best practices for API design include acceptance and response to JSON, usage of nouns instead of verbs in endpoints, versioning, documentation, using HTTP methods, and using HTTP status codes. API design patterns like sorting, pagination, filtering, and hypermedia links are also used to facilitate development and provide a better user experience. A well-designed API can improve implementation, facilitate development, and provide a better user experience.