WHOIS (RFC 3912) was just "open a TCP socket on port 43 and send a text query, get text back." Format was ad-hoc per registry. RDAP (RFC 9082) defines a REST API returning JSON, with standard fields and consistent redirects between the five RIRs.
IPFerret's WHOIS tool uses RDAP under the hood. You can query any IP at /whois/<address>.
Try it on IPFerret
See also