Crafting, testing, and maintaining events and synchronous APIs represent one of the most challenging tasks in modern software applications. This comprehensive guide delves deeply into the intricacies of managing asynchronous and synchronous APIs using a consistent design approach. The uniqueness of this book lies in its emphasis on collaborative API design between IT and business experts, facilitated by Domain-Driven Design (DDD). It provides clear guidance on selecting the appropriate communication strategy for different scenarios, ensuring that APIs meet the evolving needs of both developers and end-users. Readers will gain valuable insights into using popular definition languages such as OpenAPI and AsyncAPI. This book offers a case study that demonstrates how the described methodologies can be applied to modernize legacy systems, ensuring compatibility with development practices. By the end of this book readers, will be equipped to design APIs that are not only technically sound but also intuitive, reliable, and adaptable to the dynamic needs of modern applications. You Will: Learn how to choose the most appropriate communication strategy for different scenarios, considering factors such as scalability, reliability, and compatibility with modern development practices. Explore the practical application of popular definition languages like OpenAPI and AsyncAPI to create robust APIs Learn how to facilitate collaborative API design between IT and business experts using Domain-Driven Design (DDD), ensuring that APIs align with both technical requirements and business objectives. This book is for: Software architects, business analysts, developers and IT professionals