Which API documentation format is essential for building a custom connector quickly?

The OpenAPI definition file is essential for building a custom connector quickly because it provides a standardized way to describe the capabilities of an API. This format outlines all the details required to interact with the API, including endpoints, request and response formats, authentication methods, and data models.

By using OpenAPI specifications, developers can automate the generation of code and user interfaces, which streamlines the process of creating connectors. This is particularly advantageous in Power Automate, where having a clear and concise API definition enables the platform to efficiently understand and facilitate interactions with external services.

The other formats, while useful in specific contexts, do not offer the same level of structured detail and utility in creating connectors. JSON and XML can describe data structures but are not designed to provide comprehensive API documentation. Markdown can be used for documentation purposes but lacks the formal structure needed for automated tools to process and utilize the information effectively for building functional connectors.