The National Data Catalog stores metadata about data sets and APIs published by all leves of government. It helps developers search for, identify, and work with data sources that would otherwise take significant effort to track down.
Currently, the National Data Catalog consists of a web front-end that is powered by an API back-end.
The API is RESTful and speaks JSON. It will throw appropriate HTTP status codes on errors, along with a helpful error message passed as a JSON object.