Domain availability / RDAP lookup / WHOIS replacement / domain registration checker / expiry date lookup. Returns is_registered, registrar, registration date, expiry date, days_until_expiry, and current EPP status flags for any TLD that supports RDAP (effectively all gTLDs and most ccTLDs). Backed by rdap.org, the public RFC-7480-compliant aggregator. 404s map to is_registered: false rather than an error.