What is an .io domain?

If you’re looking to register a new web address it can be a struggle to choose a suitable ending from the many options available. Domain providers today offer over 1,500 top-level domains (TLDs) for the most diverse applications. They can represent a country or a language, are intended for special organizations and institutions, or indicate a specific focus area of a web project. One TLD that has enjoyed popularity for some time is the domain .io, whose original meaning as a country-specific extension plays little role in its success. But what does .io mean? And why is the domain extension so popular in IT circles and among tech start-ups?

Every address that is resolved with the help of the domain name system (DNS), which is the foundation of the world wide web, can be broken down into several components. These individual components always follow a clear, hierarchical structure. The highest, visible hierarchical level is called the top-level domain, or TLD for short. Since this level is always found on the far right of the address, it is also known as the “domain ending”. In the case of the web address www.example.org, for example, the “org” represents the top-level domain.

The allocation of the more than 1,500 available TLDs is regulated by ICANN (Internet Corporation for Assigned Names and Numbers), a division of the non-profit organization IANA. In principle, a distinction must be made between two different types of domain extensions: Generic top-level domains (gTLDs) such as .beauty or .blog with a topic-specific background and country-specific ccTLDs (country code top-level domains) such as .us or the .io extension discussed here.

The domain extension .io is a ccTLD, i.e., a country-specific, top-level domain, which was assigned to the British Indian Ocean Territory and introduced in 1997. The domain is administered by the domain registrar Internet Computer Bureau (ICB), which is based in the United Kingdom and since 2017 has been a subsidiary of the American group Afilias, which also administers the TLDs .info, .mobi, and .pro, among others.

From the very beginning, the .io domain was not meant to be a country-specific extension – which is not surprising given the fact that there are no legal permanent residents of the British Indian Ocean Territory. As such, any individual or legal entity can register a .io address regardless of residency or establishment, and 2 to 63 alphanumeric characters may be used. Only addresses with second-level domains like .com, .net, or .gov are blocked. In other words, registering a domain like mybusiness.net.io is not possible.

Originally, the domain .io stood for Indian Ocean. However, nobody associates the top-level domain with the British overseas territory, the last remnant of which is the Chagos archipelago (a group of islands spanning around 40 sq mi). Probably hardly anyone who asks themselves the question “What does .io stand for?” is even aware that the TLD has a country-specific background.

So, instead of asking “What does .io stand for?” the question is rather “What meaning is attributed to the .io domain?”. Here, the following two functions of the domain can be highlighted as possible answers:

• Input/output (I/O or IO): In computer science, the abbreviation I/O or IO stands for input/output, i.e., the communication of information systems such as computers with the outside world. Similar to the generic TLD .app, for example, which is the perfect extension for developers of mobile apps, the .io domain is of particular interest for tech companies in light of this possible meaning.
• Domain hacks: The top-level domain .io is also significant as an ending for domain hacks. With a little creativity, web addresses such as rad.io or portfol.io can be generated using the clever combination of ending and domain name. A popular example is the domain rub.io, which the American politician Marco Rubio used for his election campaign in the 2016 presidential race.

According to numbers published by w3techs.com approximately 0.5% of all websites are registered under the TLD .io (status: April 2021), achieving similar rankings with country-specific domains like .it (Italy) or .pl (Poland).

Its big popularity is mainly due to the meaning of the letter combination IO. Potential users such as developers or IT administrators, who are active in the IT sector, get a good idea of what the content of the site relates to simply by looking at the input/output abbreviation present in the domain. On the other hand, the domain extension also represents an easily readable and pronounceable alternative to classic, high-in-demand top-level domains and is therefore a good option if a desired name isn’t available anymore under .com etc.

The .io domain has steadily gained in importance in recent years. The original country-code domain ending is now at home in the tech world as well as being in demand for fun, play-on-words addresses and web projects that don’t have anything to do with IT and technology. Below, we compare the most important advantages and disadvantages of a .io TLD: