A reserved domain is withheld from ordinary registration for a technical or policy purpose. IANA maintains example.com, example.net and example.org for documentation. Special-use suffixes include .test, .invalid and .localhost. Individual TLD registries also reserve labels for operations, countries, protected organizations or local policy.
Registrar search results flatten several states into one word: “unavailable.” That can mean an ordinary customer owns the domain, the registry charges a premium, the label is blocked, or the name was never allocatable. A registration-data lookup may not clarify the last three. Understanding the reservation layer prevents wasted acquisition attempts and unsafe examples.
Four different kinds of unavailable name
| State | Who controls it | Can you buy it? | Example |
|---|---|---|---|
| Registered | Current registrant under registry rules | Only if released, expired or transferred by agreement | openai.com |
| Protocol special-use | IETF designation recorded by IANA | Not as an ordinary public domain | anything.invalid |
| IANA documentation name | IANA | No registration or transfer | example.com |
| Registry-reserved label | The TLD registry under policy or contract | Usually no; release rules vary | A country name or registry-operations label |
| Premium inventory | Registry or registrant | Potentially, at a special price | A short dictionary word |
“Reserved” should not be used as a synonym for every unavailable name. A premium domain is priced differently but still allocatable. A registered domain has an owner. A reserved label may never enter the ordinary pool, or may be released only after a policy approval.
The safe example domains
Technical writing needs realistic addresses without sending readers to a stranger’s website. RFC 2606 and later special-use work provide that safety. IANA maintains example.com, example.net and example.org for illustrative use, and they are not available for registration or transfer.
You can build subdomain examples beneath them:
api.example.comfor an API host;mail.example.orgfor an email or DNS example;customer.example.netfor a tenant subdomain; andhttps://www.example.com/docs?id=42for a complete URL.
Do not improvise a plausible real domain
A name that is unregistered today can be registered tomorrow. Documentation then sends users, credentials or automated traffic to someone else. Use the designated example domains rather than a made-up .com.
Special-use names are not interchangeable
IANA maintains the Special-Use Domain Names registry. A listing applies to the named domain and its subdomains, but each entry’s referenced standard defines what software should do. “Special use” does not mean every name resolves locally or is safe for the same experiment.
| Name | Intended role | Useful caution |
|---|---|---|
.test | Controlled testing | Requires an appropriate test environment; no public site is created |
.invalid | A name intended to be obviously invalid and not resolve normally | Best when failure is the point of the example |
.localhost | Loopback-host naming | Application behavior can depend on the relevant standard and implementation |
.example | Documentation at the TLD level | For examples, not production |
.local | Multicast DNS | Using it as an ordinary private DNS suffix can create conflicts |
home.arpa | Residential home-network naming | Prefer it over inventing a private suffix for that defined use |
.onion | Tor onion services | It is not an ordinary DNS TLD |
The registry changes as standards evolve, so consult IANA’s current table before designing a protocol or private namespace. A suffix copied from an old tutorial may now collide with a delegated TLD or have a newer defined behavior.
Why a TLD registry reserves second-level labels
At label.tld, the registry for that TLD decides which labels may be allocated within its policy. Generic TLD agreements require categories of protected names, which can include ICANN- and IANA-related strings, country and territory names, some international organizations, and labels used to operate the registry. Two-character labels and protected identifiers have their own release mechanisms and exceptions.
Country-code registries set their own local policies. A ccTLD may reserve names of provinces, municipalities, government bodies or existing namespace categories. That is why a label available under .com can be blocked under .ca or .uk, and why rules cannot safely be inferred from a different extension.
Some reservations can be released after authorization; others cannot. Even when ICANN permits a generic registry to release a category, the operator may not be required to offer it. The relevant registry policy is the source of truth.
Why a lookup can show no registrant
WHOIS or RDAP describes allocated domain objects; it is not a universal availability oracle. A search with no registrant record can still be unavailable because it is:
- reserved by the registry or blocked by policy;
- premium inventory not offered through that particular registrar;
- in an expiration, redemption or deletion state;
- unsupported by the registrar you searched;
- subject to launch, claims or eligibility rules; or
- syntactically invalid under the registry’s naming policy.
Check the registry’s own search or RDAP service, another accredited registrar, the TLD policy and the domain status codes. If a valuable label appears inexplicably unavailable, ask the registry or registrar rather than assuming a hidden owner.
Safe choices for testing and documentation
| Need | Use | Avoid |
|---|---|---|
| Ordinary documentation | example.com, example.net or example.org | A plausible invented live domain |
| Guaranteed invalid-name example | A name beneath .invalid | A currently unregistered real TLD name |
| Application on the local machine | localhost where the platform supports the expected behavior | Publishing a fake public hostname |
| Home network | home.arpa according to its standard | Inventing an internal suffix that might collide |
| Public staging | A subdomain you control, access-restricted | Assuming .test will be reachable publicly |
When a system needs real public DNS, use a subdomain of a domain you control. That gives you certificates, predictable resolution and the ability to remove records. Protect staging with authentication and avoid placing secrets in the hostname.
Reserved is not the same as invalid
A name can be syntactically valid under the domain character rules and still be reserved. It can also be syntactically invalid, such as a hostname label beginning with a hyphen, without appearing on any reserved list. Availability therefore requires three separate checks: valid syntax, registry policy and current allocation state.
★ Key takeaways
example.com,example.netandexample.orgare safe documentation domains maintained by IANA..test,.invalid,.localhostand other special-use names have distinct standards-defined roles.- Each TLD registry can reserve second-level labels under its contract or local policy.
- No WHOIS or RDAP owner does not prove a name is available.
- Use a controlled subdomain when testing requires real public DNS.
Frequently asked questions
Can I register example.com?
No. IANA maintains example.com, example.net and example.org for documentation. They are not available for registration or transfer, which makes them safe to show in manuals without directing readers to an unrelated registrant.
Can I register a .test domain?
No in the public DNS. .test is designated for testing under the special-use rules. Software and private environments must still be configured correctly; the reservation does not create a public website or automatically route a local test name.
What is the difference between reserved and registered?
A registered domain has been allocated to a registrant. A reserved name is withheld under technical or policy rules and may have no ordinary registrant. Both can appear unavailable at a registrar, but the reason and possibility of future release differ.
Why does WHOIS show no owner when a domain is unavailable?
The label may be reserved, blocked, premium, subject to registry policy, unsupported by that registrar, or temporarily held in a lifecycle state. Registration-data absence is not proof that the name can be bought.
Which domain should I use in documentation?
Use example.com, example.net or example.org for ordinary examples, or names beneath them such as api.example.com. Use .invalid when an example must be guaranteed not to resolve. Select special-use names only when their defined behavior matches the test.