Domain availability APIs compared, and what each one will not tell you
11 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 |
| Fastly Domain Research API | No | Yes | No | Not documented | Not documented |
| Vercel Domains Registrar API | No | No | Yes | Not documented | Not documented |
| DomScan | No | Yes | Not documented | Not documented | Yes |
| WhoisXML API Domain Availability | No | Not documented | Not documented | Not documented | Partly |
| WhoisJSON | No | Not documented | Not documented | Not documented | Yes |
| Whose.Domains | Partly | Not documented | No | Not documented | Not documented |
| GoDaddy Domains API | Partly | Not documented | Partly | Not documented | Yes |
| Domainee | Yes | Not documented | No | Not documented | Not documented |
| rdapapi.io | No | Not documented | No | 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.
Being callable by an assistant is no longer the difference
It was, on the documentation we read in July 2026, and it stopped being one inside a month: GoDaddy publish a remote MCP server that needs no account and no credential, and WhoisJSON ship one you run locally with your key. The row is still worth reading, because what reaches the assistant is not the same in each case — theirs answers whether a name is taken, and GoDaddy's documentation says it returns no prices at all. Ours carries the renewal, the minimum term and the registration policy into the same answer. That is the claim to check, and the table above is where it can be.
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
- https://www.fastly.com/products/mcp-server, read 2026-07-31
Fastly Domain Research API
The product Domainr's own documentation points at, sold as two endpoints: algorithmic domain suggestion, and a status check in either a registry-level or a DNS-and-aftermarket scope.
What it does better than dotsweep
- Two availability scopes, priced separately: a registry-level Precise check and a cheaper DNS-and-aftermarket Estimated one. A caller chooses how much certainty to pay for, where we make that choice for you.
- Algorithmic domain suggestion across extensions and domain hacks, which is a different product from availability and one we do not offer at all.
- An ICANN-accredited registrar, a commercial support relationship and an invoice, none of which we have.
dotsweep compared with Fastly Domain Research API in full →
- https://www.fastly.com/products/domain-research-api, read 2026-08-01
- https://www.fastly.com/documentation/reference/api/domain-management/domain-research/, read 2026-08-01
- https://docs.fastly.com/products/domain-research-api, read 2026-08-01
- https://www.fastly.com/pricing, read 2026-08-01
- https://www.fastly.com/products/mcp-server, read 2026-07-31
Vercel Domains Registrar API
A registrar API inside the platform the caller is probably already deploying to, covering availability, pricing, purchase, transfer, renewal and nameservers.
What it does better than dotsweep
- Registration, renewal and transfer prices come from the registrar that will actually sell you the name, with an explicit term, so the quote and the checkout cannot disagree. Ours comes from a wholesale feed.
- It completes the purchase. Availability, buying, transferring, nameservers and auto-renewal are one API and one account, where we stop at telling you the name is free and hand you a link.
- If the project already deploys on Vercel, the domain arrives attached to it with nothing further to wire up.
dotsweep compared with Vercel Domains Registrar API in full →
- https://vercel.com/changelog/new-domains-registrar-api-for-domain-search-pricing-purchase-and-management, read 2026-08-01
- https://vercel.com/docs/domains/registrar-api, read 2026-08-01
- https://vercel.com/docs/rest-api/reference/endpoints/domains-registrar/get-availability-for-a-domain, read 2026-08-01
- https://vercel.com/docs/rest-api/reference/endpoints/domains-registrar/get-price-data-for-a-domain, read 2026-08-01
DomScan
A broad domain, DNS, WHOIS and security intelligence catalogue, priced in credits, with availability as one endpoint among several dozen.
What it does better than dotsweep
- A documented third state for availability: the availability field is typed boolean or null, with a confidence field, an error field and a whole summary object accounting for ambiguous and heuristic results. That is a finer-grained report of its own uncertainty than ours.
- Several dozen endpoints past availability, covering WHOIS, DNS, SSL, typosquatting, reputation, monitoring and bulk datasets, where we answer three questions and stop.
- A monthly allowance stated as one number a bulk job can be budgeted against, and credit packs that do not expire, rather than a per-minute rate a job has to be paced against.
dotsweep compared with DomScan in full →
- https://domscan.net/docs/check-availability, read 2026-08-01
- https://domscan.net/pricing, read 2026-08-01
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
- https://main.whoisxmlapi.com/ai/mcp-server, read 2026-07-31
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, which a one-off bulk job can be planned against in one sum. Ours is a per-minute rate with no monthly ceiling, so the same job has to be paced instead of budgeted.
- 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
- https://whoisjson.com/mcp, read 2026-07-31
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.
- A remote MCP server that needs no account and no credential, which is the same position we occupy on the one column we expected to hold alone, from a registrar with a name a buyer already trusts.
dotsweep compared with GoDaddy Domains API in full →
- https://developer.godaddy.com/doc/endpoint/domains, read 2026-07-30
- https://developer.godaddy.com/en/docs/api-users/mcp, read 2026-07-31
Domainee
A custom-domains product for SaaS platforms, which publishes its availability checker as a free public endpoint with no key.
What it does better than dotsweep
- Keyless and CORS-enabled, so it can be called directly from a browser with no proxy in between. That is the column we expected to hold alone, and this is a second product holding it.
- It resells the name. Their wider product buys and attaches domains on behalf of a SaaS platform's own end users, which is a business we are not in.
- A per-IP allowance published as two plain numbers, a minute rate and a daily ceiling, rather than a rate a caller has to infer the daily consequence of.
dotsweep compared with Domainee in full →
- https://domainee.dev/docs/free-apis/domain-availability-checker, read 2026-08-01
rdapapi.io
An RDAP lookup service returning normalised JSON for domains, IP networks, ASNs and entities. Availability is implied by whether a record comes back, rather than returned as a verdict.
What it does better than dotsweep
- IP networks, ASNs and entities as well as domains, which are three lookup types we do not answer at all and which RDAP was designed to carry.
- A follow parameter that chases thin-registry referrals to get registrant and technical contacts, where our WHOIS drawer reports only what the first response held.
- A documented no-overage policy: exceeding the monthly quota returns 429 rather than producing an invoice nobody agreed to.
dotsweep compared with rdapapi.io in full →
- https://rdapapi.io/, read 2026-08-01
Questions people actually ask
Which domain availability API works without an API key or an account?
dotsweep and Domainee: yes. Whose.Domains and GoDaddy Domains API: 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, Domainr, Fastly Domain Research API and DomScan: yes. WhoisXML API Domain Availability, WhoisJSON, Whose.Domains, GoDaddy Domains API, Domainee and rdapapi.io 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 and Vercel Domains Registrar API: yes. GoDaddy Domains API: partly. DomScan, 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. Fastly Domain Research API, Vercel Domains Registrar API, DomScan, WhoisXML API Domain Availability, WhoisJSON, Whose.Domains, GoDaddy Domains API, Domainee and rdapapi.io 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, Fastly Domain Research API, DomScan, WhoisXML API Domain Availability, WhoisJSON, Whose.Domains and Domainee: partly. Vercel Domains Registrar API and GoDaddy Domains API do 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 10 domains each. No daily or monthly ceiling and no credit balance, so the rate is the whole quota. Edge cache hits are not counted at all.
Which domain availability API can ChatGPT or Claude call directly?
dotsweep, DomScan, WhoisJSON and GoDaddy Domains API: yes. WhoisXML API Domain Availability: partly. Domainr, Fastly Domain Research API, Vercel Domains Registrar API, Whose.Domains, Domainee and rdapapi.io do not document it on the pages we read, which is not the same as not doing it.
dotsweep: A remote MCP server at /mcp over the same handlers, addable as one URL with no account and no key, plus /llms.txt so an assistant that only fetches can still call it.
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 →