Domain availability APIs compared, and what each one will not tell you
Six domain availability APIs compared on the four things a buyer decides: whether you can call it without a key, whether it admits when a registry was unreachable, whether it returns the renewal price and minimum term, and whether it says who may register. Every claim cites the vendor's own documentation and the date it was read.
Availability is the easy half. Every product here answers whether a name is taken. They differ on the three questions that follow it, which are what the name will actually cost you over time, whether you are permitted to register it, and what the answer says when the registry could not be reached.
| Product | No key | Admits doubt | Renewal + term | Eligibility | Assistant-ready |
|---|---|---|---|---|---|
| dotsweep this site | Yes | Yes | Yes | Partly | Yes |
| Domainr deprecated | No | Yes | No | Partly | Not documented |
| WhoisXML API Domain Availability | No | Not documented | Not documented | Not documented | Not documented |
| WhoisJSON | No | Not documented | Not documented | Not documented | Not documented |
| Whose.Domains | Partly | Not documented | No | Not documented | Not documented |
| GoDaddy Domains API | No | Not documented | Partly | Not documented | Not documented |
Hover or tap any answer for the sentence behind it. Nothing in this table is a score, and there is no total: the rows are different products for different jobs, and adding up ticks would invent a ranking the data does not support.
Why "the most established option" is not the safe answer here
Ranked by track record and integrations, this category has an obvious winner, and it is the one whose vendor is moving customers off it. Domainr's own documentation says the v2 API is deprecated and points to a different product after the 2023 Fastly acquisition. Established is a fact about a product's past. It is not the same as the product you should call from code you are writing today, and it is the column that most confidently gets that wrong.
What we do not compete on
Extension count is the number every vendor here leads with, and we lose it badly: WhoisXML tracks 7,596 or more, and we have read the registration policy of 38. The count answers a question almost nobody has. If your name is a .com, one extension is enough, and if it is not, what you need to know is whether you are eligible and what the renewal costs, which is where a large list is usually silent.
We also do not do domain intelligence. Certificate data, WHOIS history and reputation scoring are real work and Whose.Domains does them; we answer whether a name is free, what it costs and who may register it, and nothing else.
The products
Domainr (Fastly)
A domain search and status API with a twenty-value status vocabulary that covers aftermarket and registry-reserved states as well as plain availability.
Their own documentation says the v2 API is deprecated, that Domainr was acquired by Fastly in 2023, and that users are encouraged to migrate to the Fastly Domain Research API.
What it does better than dotsweep
- Twenty status values against our three, including aftermarket states such as
marketed,transferableandexpiringthat we do not model at all. - A documented state for its own uncertainty, which most of this list does not have.
- Years of production use behind other people's domain search tools, which is a track record we do not have.
dotsweep compared with Domainr in full →
- https://domainr.com/docs/api, read 2026-07-30
- https://domainr.com/docs/api/v2/status, read 2026-07-30
WhoisXML API Domain Availability
An availability endpoint inside a broader domain-intelligence product, returning XML or JSON across a very large extension list.
What it does better than dotsweep
- 7,596+ TLDs and ccTLDs tracked, against the 38 whose registration policy we have actually read.
- One account covers WHOIS, DNS and the rest of their domain-intelligence range, where we answer availability, price and eligibility and nothing else.
- A commercial support relationship and an invoice, which matters for anything a business depends on.
dotsweep compared with WhoisXML API Domain Availability in full →
- https://domain-availability.whoisxmlapi.com/api, read 2026-07-30
WhoisJSON
A WHOIS and availability API with a small JSON response, sold on how little you have to parse.
What it does better than dotsweep
- A stated monthly allowance of 1,000 requests. Ours is a per-minute rate limit with no published monthly total, which is harder to plan against.
- Several other lookup services under the same key and the same allowance.
- They publish a comparison of this whole category, which is more than most vendors here do and more than we did until now.
dotsweep compared with WhoisJSON in full →
- https://whoisjson.com/documentation, read 2026-07-30
- https://whoisjson.com/blog/best-domain-availability-api, read 2026-07-30
Whose.Domains
A free domain-intelligence API covering WHOIS, DNS records, domain history, SSL certificate data and a domain score, with availability as one search type inside a bulk endpoint.
What it does better than dotsweep
- Domain history with WHOIS diffs, SSL certificate data, reverse IP and a health score, none of which we return.
- Free with no invoice and no account for the open endpoints, which is the same position we occupy.
- Expiring-domain discovery, which is a different question from availability and one we do not answer.
dotsweep compared with Whose.Domains in full →
- https://whose.domains, read 2026-07-30
- https://whose.domains/api-docs, read 2026-07-30
GoDaddy Domains API
A registrar's own availability endpoint, returning whether the name is free and what that registrar will charge for the first term.
What it does better than dotsweep
- The price comes from a registrar that will actually sell you the name, so the quote and the checkout cannot disagree. Ours comes from a wholesale feed.
- Availability, price and purchase happen through one vendor and one account.
- If you are already a GoDaddy customer there is nothing new to integrate.
dotsweep compared with GoDaddy Domains API in full →
- https://developer.godaddy.com/doc/endpoint/domains, read 2026-07-30
Questions people actually ask
Which domain availability API works without an API key or an account?
dotsweep: yes. Whose.Domains: partly.
dotsweep: No key, no account, no signup. curl https://dotsweep.com/check/example.com works from a cold start.
Which domain availability APIs can tell you a registry was unreachable?
dotsweep and Domainr: yes. WhoisXML API Domain Availability, WhoisJSON, Whose.Domains and GoDaddy Domains API do not document it on the pages we read, which is not the same as not doing it.
dotsweep: A registry that is throttled, timed out or publishes no RDAP resolves to estimated, never available. A 429 from one registry does not become a confident answer about another one on the same host.
Which domain availability API returns the renewal price and the minimum term?
dotsweep: yes. GoDaddy Domains API: partly. WhoisXML API Domain Availability and WhoisJSON do not document it on the pages we read, which is not the same as not doing it.
dotsweep: Registration and renewal are separate figures, a first-year discount is flagged as a promotion, and an extension the registry sells only in multi-year terms is multiplied out so the leading number is what leaves your account.
Which domain availability API tells you whether you are allowed to register the name?
dotsweep and Domainr: partly. WhoisXML API Domain Availability, WhoisJSON, Whose.Domains and GoDaddy Domains API do not document it on the pages we read, which is not the same as not doing it.
dotsweep: 38 extensions have had their registry policy read, 33 of them with an eligibility rule, each citing the registry's own page and the date it was read. An extension that is not in that set asserts nothing.
What do these domain availability APIs give you for free?
dotsweep: yes. Domainr, WhoisXML API Domain Availability, WhoisJSON and Whose.Domains: partly. GoDaddy Domains API does not document it on the pages we read, which is not the same as not doing it.
dotsweep: 120 requests a minute, counted as requests rather than domains, and a batch endpoint carrying 20 domains each. Edge cache hits are not counted at all.
Which domain availability API can ChatGPT or Claude call directly?
dotsweep: yes. Domainr, WhoisXML API Domain Availability, WhoisJSON, Whose.Domains and GoDaddy Domains API do not document it on the pages we read, which is not the same as not doing it.
dotsweep: An MCP server at /mcp over the same handlers, plus /llms.txt, so an assistant can call it without a wrapper.
How we know this, and what we did not do
Every claim about another product here was read from that vendor's own documentation, and each one is listed with the page and the date it was read. No figure comes from a review, a listicle or another comparison.
We did not benchmark any of these services. Nothing on this page reports a measurement, and where a row says "not documented" it means their documentation did not answer the question and we did not test it. It is not a quiet way of saying no. Getting that distinction wrong is how the rest of a comparison table stops being worth reading, and it is the same rule the rest of this site follows about extensions whose registry policy nobody has read.
If something here is out of date or wrong, the date next to it is there so you can tell which, and support@dotsweep.com reaches a person.
Try the one that needs no signup
There is nothing to create an account for, so the fastest way to judge this is to run it:
curl https://dotsweep.com/check/example.comAPI and MCP reference → · Extensions with registration requirements → · What a domain actually costs →