Domain Checker

Check domain availability in bulk using RDAP (Registration Data Access Protocol) as the primary signal, with WHOIS and DNS fallbacks. Python stdlib only.

When to Use

• User asks "is <domain> available / taken / registered?"
• User wants to check many domains at once (a list, a file, names piped in)
• User wants to test a brand name across many TLDs (acme.com, acme.net, acme.io, …)
• User wants machine-readable output (CSV/JSON) for further processing
• User wants only available (or only taken) results filtered

Do NOT use for: WHOIS contact lookup (this skill only checks existence), DNS record inspection (use dig), trademark/legal availability (this only checks registration status).

How It Works

1. RDAP first — fetches the IANA RDAP bootstrap (data.iana.org/rdap/dns.json, cached 24h in ~/.cache/domain-checker/) to find the authoritative RDAP server for each TLD. HTTP 404 = available, HTTP 200 = taken.
2. WHOIS fallback — if RDAP is unavailable for a TLD (notably .io, some ccTLDs) or returns ambiguous, shells out to the local whois CLI and matches well-known "not found"/"registered" patterns.
3. DNS — optional, weak signal. Resolves A/AAAA records. Confirms "taken" only — registered-but-unhosted domains will show no DNS, so DNS alone cannot prove "available".