An API is available for data.overheid.nl that makes the metadata of all available datasets available. All information on data.overheid.nl can be reused under the CC-0 license.
Technical manuals are available that are intended for developers who want to make the data of data.overheid.nl accessible. An explanation of how the API works is included on the CKAN website: https://docs.ckan.org/en/latest/api/index.html
Please note: the CKAN API v3 is not a REST API. There is no complete OPEN API spec yet for the CKAN API version 3.