How to Check Domain Availability in Bulk — Free, No API Keys

Every registrar's search box checks one name at a time, and it logs what you type — which is exactly why serious domain hunters avoid it for brainstorming. Paid APIs (WhoisXML, DomainTools) solve bulk checking but start around $19/month and keep query logs. There is a third way: RDAP, the public JSON successor to WHOIS, called directly from your browser.

Why bulk checking works without a server in 2026

Registries like Verisign (.com/.net), Google Registry (.dev/.app/.page), Identity Digital (.io/.ai/.me), CentralNic and Radix expose RDAP over HTTPS with permissive CORS headers. An HTTP 200 means the domain is registered; a 404 means it is not in the registry. Because CORS is open, a plain web page can call these endpoints directly — no backend, no API key, no proxy.

How to run a bulk check, step by step

1. Open Domain Hunter (free, open-source, runs in your browser).
2. Paste your candidate names — one per line, up to 3,000. URLs and paths are cleaned automatically.
3. Pick zones: 140+ TLDs are curated (from com and dev to so and ly), and new gTLDs are discovered via the live IANA registry map.
4. Press Check availability. Results stream in with status, first-year price, renewal and 3-year TCO; export everything to CSV.

Is an “available” result trustworthy?

For ICANN-contracted gTLDs an RDAP 404 is authoritative. Some ccTLDs have less reliable RDAP, so a good tool corroborates with DNS (NS lookups over DNS-over-HTTPS) and reports probably available instead of overpromising. And remember: availability is a snapshot — a name can be registered seconds after you check it.

Staying polite to registries

RDAP is the registries' own public interface, and bulk use is fine when rate-limited: per-registry spacing, exponential backoff on HTTP 429, and honoring Retry-After. Google Registry, for example, is capped near one request per second.

Source code (MIT): github.com/WhiteBite/Domain-Hunter