RDAP, the successor to WHOIS
RDAP (Registration Data Access Protocol) is gradually replacing the old WHOIS protocol. Same data — holder, dates, name servers — but structured, and fetched straight from the competent registry (RIPE, ARIN, Verisign…).
What you will not see
Since GDPR, personal details of domain holders are largely redacted. For an IP address, the registry returns the organization managing the range — your ISP for instance — never the individual subscriber.