Availability checking: WHOIS and RDAP
How to check whether a domain is available in five seconds, what WHOIS / RDAP actually returns, and why REDACTED is normal.
Domain availability is the most common single check you’ll run in this course. A client asks for a name; you need to know whether it’s available, registered, premium-priced, or reserved. The registrar’s panel will tell you, but it’s worth knowing how to check from a terminal in 5 seconds without logging into anything.
WHOIS is the classic tool. RDAP is the modern replacement. Web-based lookups are the universal fallback.
WHOIS, the classic tool
WHOIS is a protocol from the 1980s for querying domain registration information. The command-line tool is also called whois and is installed on most Linux/macOS systems. On Windows it’s available via Sysinternals whois.exe, in WSL, or via online services.
| 1 | $ whois example.com | |
| 2 | Domain Name: EXAMPLE.COM | |
| 3 | Registry Domain ID: 2336799_DOMAIN_COM-VRSN | |
| 4 | Registrar WHOIS Server: whois.iana.org | |
| 5 | Registrar URL: http://res-dom.iana.org | |
| 6 | Updated Date: 2024-08-14T07:01:34Z | |
| 7 | Creation Date: 1995-08-14T04:00:00Z | |
| 8 | Registry Expiry Date: 2025-08-13T04:00:00Z | |
| 9 | Registrar: RESERVED-Internet Assigned Numbers Authority | |
| 10 | Domain Status: clientDeleteProhibited | |
| 11 | Domain Status: clientTransferProhibited | |
| 12 | Domain Status: clientUpdateProhibited | |
| 13 | Name Server: A.IANA-SERVERS.NET | |
| 14 | Name Server: B.IANA-SERVERS.NET | |
| 15 | Registrant Name: REDACTED FOR PRIVACY | |
| 16 | Registrant Email: Please query the RDDS service of the Registrar of Record |
For most days, WHOIS gives you four useful things at a glance: registrar, status flags, registration and expiry dates, and nameservers.
RDAP, the modern replacement
RDAP (Registration Data Access Protocol) is the post-GDPR replacement for WHOIS. Structured JSON output, standardised across registries, supports authentication and access control, designed to handle GDPR-style redaction cleanly.
Many registries publish RDAP services at predictable URLs. The IANA RDAP bootstrap registry maps TLDs to RDAP servers. Most modern whois tools fall through to RDAP automatically if WHOIS is unavailable or restricted; you only reach for RDAP directly when you’re scripting against the data.
Web-based lookups when terminal isn’t available
When you don’t have a terminal handy (working in a client’s locked-down environment, on someone else’s machine), most registrars expose a search box on their site. The registrar’s check availability search is the same query in a friendlier wrapper. The data is the same; the presentation often layers marketing on top of the result (would you like to register alternatives?).
The GDPR redaction reality
What this is NOT
- “REDACTED means available.” Opposite. Redacted means registered with hidden contacts. Available means no registration exists.
- “The registrar’s search alone is enough.” The registrar’s panel will show not available for premium, reserved, and registered domains without distinguishing. WHOIS / RDAP is what you check when you need the why.
- “WHOIS contact data is always current.” Even when not redacted, the contact data is what the registrant last set. Stale data is common.
Decision walkthrough
Follow-up: WHOIS shows bestcoffee.com registered since 2003, registrant redacted, registrar GoDaddy, expiry 2027. The client asks you to reach out to the owner. The redaction blocks direct WHOIS-based contact; legitimate outreach paths exist. Surface the options: contact form via the domain’s own site if it has one, GoDaddy’s domain-broker service (paid, GoDaddy reaches out on the client’s behalf), a third-party broker, or back-order for 2027 expiry. Get the client’s decision on which path before acting.