To fully exploit the business opportunity available through application programming interfaces (APIs), your designers must consider each API's purpose and audience as they answer a wide range of technical design questions. Beyond choice of messaging type (e.g., REST and SOAP), it's important to foster API acceptance by ensuring that your designers know how to meet an API's functional requirements with clear designs that appropriately consider the nuances of transaction processing, error handling, and related concerns. As part of a series on API design practices, this report examines best practices for ensuring that detailed API designs are readily understandable and support robust solutions.