RDAP vs WHOIS: What Developers Need in 2026
Compare RDAP and WHOIS protocols, response formats, bootstrap discovery, and the ICANN transition—choose the right domain lookup stack.
RDAPWHOISdomain lookupICANNJSON API
At a glance
WHOIS is a legacy text protocol (often TCP port 43) with inconsistent output. RDAP returns structured JSON over HTTPS per RFC 9082/9083.
- Transport: WHOIS is often cleartext; RDAP uses TLS.
- Parsing: WHOIS needs regex; RDAP is machine-readable JSON.
- Discovery: RDAP uses the IANA bootstrap registry (RFC 9224).
- Access: RDAP supports tiered access and explicit redaction notices.
Why RDAP first
Since January 28, 2025, ICANN no longer requires gTLD operators to run port-43 WHOIS. New tooling should treat RDAP as primary and WHOIS as fallback.
Recommendations
- Automate with RDAP JSON; keep WHOIS port 43 as compatibility layer.
- Use standardized status, events, and links for security workflows.
- Cache responses and honor rate limits (HTTP 429).