An API (application programming interface) is a set of routines, protocols, and tools for building software and applications.
Openaid.se uses the API from the IATI Datastore, which you can find here: datastore.iatistandard.org/docs/api/. Through that API you can access all IATI data, not just the files from Sweden that we use on Openaid.se
There is also an API for the IATI Registry, which contains meta-data on files published in the IATI XML format. You can access that here: iatiregistry.org/registry-api