The backbone of Splunk has always been the underlying REST API. The REST API allows access to everything from searching, to configuration, to ingesting data. Whether it's running one-off scripts to extract some data or automating a workflow with a third-party system, it can all be done with simple web requests to the API.
As with most of Splunk, the REST API is also very flexible and can many parameters that you can manipulate to change the output types (JSON, XML, and so on) or filter the results. Long before Splunk had the web framework, the REST API was the workhorse of integrating with Splunk and still plays a big part in this.
