Introduction[Link]
RDAP is a protocol to query registration data. It is the successor of WHOIS and has many advantages over WHOIS, including:
internationalisation
authentication and authorisation
it enables roles-based access to attributes
searching
The protocol is built upon a REST API and is standardised in RFC 7480, RFC 7481, RFC 9082, RFC 9083 and RFC 9224
There are a lot of clients specifically implemented for RDAP, but you can invoke RDAP queries by using curl or wget.
Example:
curl https://rdap.nic.brussels/domain/nic.brussels
When invoking RDAP calls programmatically, in general we advise you to look for a generic REST client to invoke the RDAP calls.