Which of the following defines the characteristics of an API in MuleSoft?

The RAML (RESTful API Modeling Language) specification is a powerful tool for defining the structure, behavior, and characteristics of an API in MuleSoft. It allows developers to create a clear and structured description of their APIs in a human-readable format, making it easier to understand the endpoints, request/response types, and other details necessary for implementing the API.

Using RAML, developers can specify various aspects such as resource types, data types, and the methods supported (GET, POST, PUT, DELETE, etc.). This not only helps in documentation but also facilitates collaboration among teams by providing a contract that various stakeholders can refer to during development.

While other options like OpenAPI Specification and WSDL documents also define API characteristics, RAML is specifically tailored for MuleSoft's Anypoint Platform and is particularly useful for creating RESTful APIs, which are commonly used in modern web services. Additionally, SOAP configurations are more relevant for SOAP-based services rather than RESTful API documentation. Therefore, RAML serves as the most suitable choice for defining an API's characteristics in the context of MuleSoft development.