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NIC.IO -- .IO Domain Registry
TLD typeCountry code top-level domain
RegistryNIC.IO (run by Internet Computer Bureau)
SponsorIO Top Level Domain Registry (Cable and Wireless)
Intended useEntities connected with  British Indian Ocean Territory
Actual usePopular with startup companies and browser games; little if anything related to the territory itself.
Registration restrictionsNone for 2nd level registrations; 3rd level registrant must be resident of British Indian Ocean Territory
StructureRegistrations are taken directly at the second level or at third level beneath various 2nd-level labels
DocumentsTerms & Conditions; Rules
Dispute policiesDispute Resolution Policy
Registry websiteNIC.io

The Internet country code top-level domain (ccTLD) .io is assigned to the British Indian Ocean Territory.[1] The domain is administered by the Internet Computer Bureau, a domain name registry company which is a subsidiary of Afilias and is based in the United Kingdom.[2]

Google's ad targeting treats .io as a generic top-level domain (gTLD) because "users and webmasters frequently see [the domain] more generic than country-targeted."[3]


The top-level domain io has existed since 1997. The first subdomain was registered in 1998, when Levi Strauss & Co. registered the domain levi.io.[4]

In 2021, the United Nation's International Tribunal for the Law of the Sea ruled that the United Kingdom has no sovereignty over the Chagos Archipelago, and that Mauritius is sovereign. This would extinguish the British Indian Ocean Territory, and the IO two-letter country code and .io could also be extinguished. The United Kingdom disputes and does not recognise the tribunal's decision, so further legal processes are likely.[5][6]


Labels for .io domains may only contain alphanumeric characters and hyphens, and must be between 3 and 63 characters long. Domain names cannot begin or end with a hyphen symbol, and may not contain two consecutive hyphens. The entire domain name may not contain more than 253 characters.[7]


The right to administer domain names is given to approved organisations by the Internet Assigned Numbers Authority (IANA). The Internet Computer Bureau (ICB) administers .io domains. This domain name registry is a British company, and operates for this purpose under the name NIC.IO. The company also holds the rights to sell the .sh and .ac domains, the top-level domains for the islands of Saint Helena and Ascension, respectively.[8]

In 2017, ICB was sold to Afilias, an American corporation, for $70 million.[9]

Registration and restrictions[edit]

Individuals and organisations are allowed to register .io domains.

Applicants for the registration of .io domains do not need to be registered or established in the British Indian Ocean Territory. Third-level domains, such as "xyz.com.io", can only be registered by an inhabitant of the area. (Since there are no legal, permanent inhabitants of the British Indian Ocean Territory, theoretically no third-level domains will be registered.) Any second-level domains used by NIC.IO and top-level domains cannot be used as a third-level domain. For example, the domains "com.com.io", "org.com.io", and "biz.com.io" are all restricted.[10]

Domain names in .io may not be used, "for any purpose that is sexual or pornographic or that is against the statutory laws of any nation." If this requirement is breached, "NIC.IO reserves the right to immediately deactivate the offending registration."[11]

.io domains may be registered for a minimum of one year, and a maximum of 5 years.[12]

Domain names in .io are priced higher than those in other TLDs. Registering an available .io-domain currently (at 3 September 2020) costs US$90 per annum.[11]


The .io domain has considerable usage unrelated to the British Indian Ocean Territory.

In computer science, "IO" or "I/O" is commonly used as an abbreviation for input/output, which makes the .io domain desirable for services that want to be associated with technology. .io domains are often used for open source projects, application programming interfaces ("APIs"), startup companies, video games, and other online services.[13][14]

The TLD is also used for domain hacks, as the letters "io" are an ending of many English terms. For example, Rub.io is a shortened URL that was used for the 2016 U.S. presidential campaign of Marco Rubio.

One reason given for the TLD's popularity is that it stands out by being shorter than other TLDs. Also, the .io TLD is less occupied than other TLDs, so it is more likely that a given term is available there.[15]

In Italian, io is the first-person singular pronoun (English "I"), which makes the domain appealing for personal websites.

In Esperanto, io as an independent word is the assertive existential indefinite pronoun (English "something"). As a suffix, -io is used to terminate official names of countries or other kind of lands under which a community of people are grouped. The Plena Ilustrita Vortaro de Esperanto include almost 500 terms like that, from Abisenio (former name of Ethiopia, Etiopio) to Zambio (Zambia). Derived from that, the suffix is also used to designate a community of people whose common interest is indicated by the suffixed root, especially in the term Esperantio, the community of speakers of the language and their culture as a whole, as well as the places and institutions where the language is used. As of May 2020, the esperant.io domain name redirects to Libera Folio, an independent generalist online bulletin written in Esperanto.

Around 2015 a multiplayer game, Agar.io, spawned many other games with a similar playstyle and .io domain, such as Diep.io, Slither.io, Surviv.io, ZombsRoyale.io, and Hole.io. Such games are collectivelly called ".io games".[16]


According to a 2014 Gigaom interview with Paul Kane, then chairman of the Internet Computer Bureau, the domain name registry is required to give some of its profits to the British government, for administration of the British Indian Ocean Territory.[17] After being questioned as a result of the interview, the British Government denied receiving any funds from the sale of .io domain names, and argued that consequently, the profits could not be shared with the Chagossians, the former inhabitants forcibly removed by the British government.[18][19]


  1. ^ IDN Code Points Policy for the .IO Top Level Domain (PDF), NIC.IO, archived from the original (PDF) on 18 December 2005, retrieved 11 December 2005
  2. ^ "IANA — .io Domain Delegation Data". iana.org. Archived from the original on 18 September 2014. Retrieved 6 September 2014.
  3. ^ "Managing multi-regional and multilingual sites". Archived from the original on 5 October 2019. Retrieved 5 October 2019.
  4. ^ "whois-search.com - domain name search - Whois Search". Retrieved 8 March 2021.
  5. ^ Harding, Andrew (28 January 2021). "UN court rules UK has no sovereignty over Chagos islands". BBC News. Retrieved 1 February 2021.
  6. ^ Mortensen, James; Bashfield, Samuel (21 January 2021). "The Diego Garcia dispute hits cyberspace". The Interpreter. Lowy Institute. Retrieved 1 February 2021.
  7. ^ RFC 1035, Domain names--Implementation and specification, P. Mockapetris (Nov 1987)
  8. ^ "Internet Computer Bureau". Archived from the original on 22 October 2014. Retrieved 29 October 2014.
  9. ^ Murphy, Kevin (9 November 2018). "Afilias bought .io for $70 million". Domain Incite. Retrieved 13 August 2020.
  10. ^ "RULES for the .IO Domain and Sub-Domains". Archived from the original on 23 October 2005. Retrieved 30 July 2005.
  11. ^ a b "NIC.IO - The Indian Ocean .IO Domain Registry and Network Information Centre". nic.io. Archived from the original on 4 August 2005. Retrieved 30 July 2005.
  12. ^ ".IO Domain Name Registration price list". nic.io. Archived from the original on 22 January 2017. Retrieved 2 October 2016.
  13. ^ Beattie, Russell (12 February 2013). "The rise of .io domains for well crafted web services". Archived from the original on 10 May 2014. Retrieved 24 April 2014. There's lots of open source projects (Redis, Brackets, Launcher), a few mobile-app landing pages (Avocado, X-Ray), a ton of new web apps and services, several conference pages (Lightning, Renaissance, Resonate) and a few older companies or organizations who've changed their name to take advantage of a cleaner .io name.
  14. ^ "IO Domains in Alexa Top 1 Million". Archived from the original on 27 May 2015. Retrieved 27 May 2015.
  15. ^ "Why are startups turning to .IO?". Name.com Blog. 17 October 2013. Archived from the original on 4 April 2017. Retrieved 5 April 2017.
  16. ^ Takahashi, Dean (2017). "The surprising momentum behind games like Agar.io". VentureBeat. Retrieved 5 May 2018.
  17. ^ David Meyer (30 June 2014). "The dark side of .io: How the U.K. is making web domain profits from a shady Cold War land deal". gigaom.com. Archived from the original on 5 September 2014. Retrieved 6 September 2014.
  18. ^ "House of Lords Summer Recess 2014 Written Answers and Statements". parliament.uk. 11 August 2014. Archived from the original on 4 April 2019. Retrieved 4 April 2019.
  19. ^ David Meyer (11 July 2014). "UK government denies receiving .io domain profits". gigaom.com. Archived from the original on 1 May 2015. Retrieved 19 May 2015.

External links[edit]