What is the primary purpose of Appian's Web API?

The primary purpose of Appian's Web API is to expose the functionality of an Appian application as a web service for external use. This allows external systems and applications to interact with and make use of the underlying business processes and data that Appian manages, facilitating integration between different platforms.

By utilizing Web APIs, developers can provide access to Appian components such as processes, records, and data, enabling them to be used in other environments or applications where they can add value. This can include making Appian services available to third-party applications, which can call the API to retrieve data, trigger processes, or interact with Appian features programmatically.

The other options focus on aspects that do not align with the core functionality of Web APIs. Custom user interfaces pertain more to the front-end development aspects of Appian rather than server-to-server interactions. Enhancing data visualization is more about report and dashboard functionalities rather than API interactions. Storing application configuration settings is associated with application management rather than the purpose of a Web API, which is fundamentally about enabling communication between systems.