Top-level domain


A top-level domain is one of the domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain. The top-level domain names are installed in the root zone of the name space. For all domains in lower levels, it is the last part of the domain name, that is, the last non-empty label of a fully qualified domain name. For example, in the domain name www.example.com, the top-level domain is.com. Responsibility for management of most top-level domains is delegated to specific organizations by the ICANN, an Internet multi-stakeholder community, which operates the Internet Assigned Numbers Authority, and is in charge of maintaining the DNS root zone.

History

Originally, the top-level domain space was organized into three main groups: Countries, Categories, and Multiorganizations. An additional temporary group consisted of only the initial DNS domain,.arpa, and was intended for transitional purposes toward the stabilization of the domain name system.

Types

IANA distinguishes the following groups of top-level domains:
Countries are designated in the Domain Name System by their two-letter ISO country code; there are exceptions, however. This group of domains is, therefore, commonly known as country-code top-level domains. Since 2009, countries with non–Latin-based scripts may apply for internationalized country code top-level domain names, which are displayed in end-user applications in their language-native script or alphabet, but use a Punycode-translated ASCII domain name in the Domain Name System.
Generic top-level domains initially consisted of.gov,.edu,.com,.mil,.org, and.net. More generic TLDs have been added, such as.info.
The authoritative list of current TLDs in the root zone is published at the IANA website at as well as .

Internationalized country code TLDs

An internationalized country code top-level domain is a top-level domain with a specially encoded domain name that is displayed in an end-user application, such as a web browser, in its language-native script or alphabet, or a non-alphabetic writing system. IDN ccTLDs are an application of the internationalized domain name system to top-level Internet domains assigned to countries, or independent geographic regions.
ICANN started to accept applications for IDN ccTLDs in November 2009, and installed the first set into the Domain Names System in May 2010. The first set was a group of Arabic names for the countries of Egypt, Saudi Arabia, and the United Arab Emirates. By May 2010, 21 countries had submitted applications to ICANN, representing 11 scripts.

Infrastructure domain

The domain.arpa was the first Internet top-level domain. It was intended to be used only temporarily, aiding in the transition of traditional ARPANET host names to the domain name system. However, after it had been used for reverse DNS lookup, it was found impractical to retire it, and is used today exclusively for Internet infrastructure purposes such as in-addr.arpa for IPv4 and ip6.arpa for IPv6 reverse DNS resolution, uri.arpa and urn.arpa for the Dynamic Delegation Discovery System, and e164.arpa for telephone number mapping based on NAPTR DNS records. For historical reasons,.arpa is sometimes considered to be a generic top-level domain.

Reserved domains

A set of domain names is reserved by the Internet Engineering Task Force as special-use domain names. The practice originated in RFC 1597 for reserved address allocations in 1994 and reserved top-level domains in RFC 2606 of 1999, with additional reservations in later RFCs. These reserved names should not be used in production networks that utilize the global domain name system.
DomainReserved byReserved for
.exampleRFC 6761use in examples
.invalidRFC 6761use in invalid domain names
.localhostRFC 6761avoiding conflict with the traditional use of localhost as a hostname
.testRFC 6761use in tests
.localRFC 6762link-local host names that can be resolved via the multicast DNS name resolution protocol
.onionRFC 7686self-authenticating names of Tor onion services
.internalICANNprivate application use
.altRFC 9476alternative namespaces

Historical domains

In the late 1980s, InterNIC created the.nato domain for use by NATO. NATO considered none of the then-existing TLDs as adequately reflecting their status as an international organization. Soon after this addition, however, InterNIC also created the.int TLD for the use by international organizations in general, and persuaded NATO to use the second level domain nato.int instead. The nato TLD, no longer used, was finally removed in July 1996.
Other historical TLDs are.cs for Czechoslovakia,.dd for East Germany,.yu for SFR Yugoslavia and Serbia and Montenegro,.zr for Zaire, and.an for Netherlands Antilles. In contrast to these, the TLD.su has remained active despite the collapse of the Soviet Union that it represents. Under the chairmanship of Nigel Roberts, ICANN's ccNSO is working on a policy for the retirement of ccTLDs that have been removed from ISO 3166.

Proposed domains

Around late 2000, ICANN discussed and finally introduced.aero,.biz,.coop,.info,.museum,.name, and.pro TLDs. Site owners argued that a similar TLD should be made available for adult and pornographic websites to settle the dispute of obscene content on the Internet, to address the responsibility of US service providers under the US Communications Decency Act of 1996. Several options were proposed including xxx, sex and adult. The.xxx top-level domain eventually went live in 2011.
An older proposal consisted of seven new gTLDs: arts, firm,.info, nom, rec,.shop, and.web. Later.biz,.info,.museum, and.name covered most of these old proposals.
During the 32nd International Public ICANN Meeting in Paris in 2008, ICANN started a new process of TLD naming policy to take a "significant step forward on the introduction of new generic top-level domains". This program envisioned the availability of many new or already proposed domains, as well as a new application and implementation process. Observers believed that the new rules could result in hundreds of new gTLDs being registered.
On 13 June 2012, ICANN announced nearly 2,000 applications for top-level domains, which began installation throughout 2013. The first seven – bike, clothing, guru, holdings, plumbing, singles, and ventures – were released in 2014. As of 2025, there are approximately 1,200 delegated generic top-level domains in the global Domain Name System, including legacy gTLDs and gTLDs introduced in the 2012 New gTLD Program.
ICANN has been gearing to roll out the subsequent round of New gTLD expansion but opening the second round of New gTLD Application window in April 2026 for 12 - 15 weeks. The first draft of New gTLD Applicant Guidebook was published on 30 May 2025 followed by the period of public comments has now been approved by the ICANN board and is now expected to be published in ICANN's website by December 2025.
ICANN has also opened up Applicant Support Program to support organizations and communities which are in need of financial support to apply for New gTLD. The application window to apply for financial support has been extended until 19th December 2025 from the original deadline of 19th November 2025. ICANN has also mandated applicants to choose a registry backend service provider from ICANN's accredited Registry Service Provider list which is expected to be published in early 2026. ICANN is publishing timely updates on their website.

Rejected domains

ICANN rejected several proposed domains to include.home and.corp due to conflicts regarding gTLDs that are in use in internal networks.
Investigation into the conflicts was conducted at ICANN's request by Interisle Consulting. The resulting report was to become known as the Name Collision issue, which was first reported at ICANN 47.

Dotless domains

Due to the structure of DNS, each node in the tree has its own collection of records, and since top-level domains are nodes in DNS, they have records of their own. For example, querying org itself returns information on its nameservers:

QUESTION
org. IN ANY
ANSWER
org. 21599 IN NS a0.org.afilias-nst.info.
org. 21599 IN NS a2.org.afilias-nst.info.
org. 21599 IN NS b0.org.afilias-nst.org.
org. 21599 IN NS b2.org.afilias-nst.org.

Dotless domains are top-level domains that take advantage of that fact, and implement A, AAAA or MX DNS records to serve webpages or allow incoming email directly on a TLD – for example, a webpage hosted on http://example/, or an email address user@example.
ICANN and IAB have spoken out against the practice, classifying it as a security risk among other concerns. ICANN's Security and Stability Advisory Committee additionally claims that SMTP "requires at least two labels in the FQDN of a mail address" and, as such, mail servers would reject emails to addresses with dotless domains.
ICANN has also published a resolution in 2013 that prohibits the creation of dotless domains on gTLDs. ccTLDs, however, fall largely under their respective country's jurisdiction, and not under ICANN's. Because of this, there have been many examples of dotless domains on ccTLDs in spite of ICANN's vocal opposition.
As of July 2025, that is the case of:
  • Uzbekistan's.uz, online at https://uz./
It's a mirror of https://cctld.uz/, albeit with an invalid certificate.
In 2023, it used to be the case of:
  • Anguilla's.ai, online at http://ai./
It simply displayed a notice that the website was no longer public.
The TLD no longer has an A or AAAA record.
Other ccTLDs with A or AAAA records, as of July 2025, include:.cm,.tk and.ws.
A similar query to orgs presented above could be made for ai, which showed A and MX records for the TLD:

QUESTION
ai. IN ANY
ANSWER
ai. 21599 IN A 209.59.119.34
ai. 21599 IN MX 10 mail.offshore.ai.
ai. 21599 IN NS anycastdns1-cz.nic.ai.
ai. 21599 IN NS anycastdns2-cz.nic.ai.
ai. 21599 IN NS pch.whois.ai.

Historically, many other ccTLDs have had A or AAAA records. On 3 September 2013, as reported by the IETF, they were the following:.ac,.dk,.gg,.io,.je,.kh,.sh,.tm,.to, and.vi.