OpenAPI, initially known as Swagger until its rebranding in 2017, is a language-agnostic specification designed to describe RESTful APIs, providing a structured framework for API documentation and development. It allows the decoupling of an API's public interface from its implementation, enabling different teams to independently define required features and technical specifications using a YAML document. This specification facilitates the generation of code stubs, documentation, and mock APIs, benefiting both design and engineering teams by promoting a design-first approach and enabling iterative API development. OpenAPI is supported by a vast ecosystem of tools and a large user base, making it a valuable resource for both novice and experienced developers. However, it is not a universal solution, as its added complexity may not suit all projects, particularly those better served by non-RESTful architectures like GraphQL or gRPC. Despite its limitations, OpenAPI remains a widely adopted standard within the API development community, backed by the Linux Foundation, and is seen as a stable and mature specification for building scalable and maintainable APIs.