What does the domain abbreviation .io stand for?
The country-specific domain ending .io is assigned to the British Indian Ocean Territory. However, it is predominantly used in IT circles and by tech startups.
What is an .io domain?
The domain .io is a ccTLD, meaning a country-specific top-level domain. However, most users aren’t directly aware of what .io stands for in terms of a country. The domain ending is assigned to the British Indian Ocean Territory and was introduced in 1997. The domain is managed by the domain registrar Internet Computer Bureau (ICB), headquartered in the United Kingdom, and since 2017 has been a subsidiary of the American company Afilias, which also administers the TLDs .info, .mobi, and .pro.
The domain ending is also referred to as a top-level domain (TLD). It represents the highest visible hierarchy level in DNS name resolution and is always found on the far right of the address.
The .io domain did not originally hold the meaning of a country-specific ending—which is unsurprising given there are no legal, permanent residents of the British Indian Ocean Territory. Any individual or entity can register a .io address regardless of residence or location, using 2 to 63 alphanumeric characters. Only addresses with second-level domains like .com, .net, or .gov are blocked. Therefore, registering a domain like mybusiness.net.io is not possible.
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What does .io mean?
Originally, the .io domain stands for “Indian Ocean.” However, the top-level domain isn’t commonly associated with the British overseas territory, whose last remnant is the Chagos Archipelago (an island group of 24.4 square miles). So, what meaning is actually attributed to the .io domain? Primarily, the domain is used for two key purposes:
- Input/Output (I/O or IO): The abbreviation I/O or IO in computer science stands for Input/Output, which refers to the communication of information systems like computers with the external world. Similar to how the generic TLD .app is the ideal ending for mobile app developers, the .io domain is particularly appealing to tech companies due to this potential meaning.
- Domain hacks: The .io top-level domain is also significant for domain hacks. With some creativity, combining it with the right domain name can create catchy web addresses like
rad.ioorportfol.io. A popular example isrub.io, which U.S. politician Marco Rubio used for his presidential campaign in 2016.
In 1998, the fashion company Levi Strauss & Co. registered levi.io, the first web address under the ccTLD .io.
Why is .io so popular in the IT sector and among tech startups?
According to the figures from w3techs.com, around 0.3 percent of all websites are registered under the TLD .io (as of April 2025).
The use of the domain is primarily due to the highlighted meaning of the letter combination IO: Potential users like developers or IT admins, who are active in the computer science industry, can see the Input/Output abbreviation in the domain as an initial indication of the thematic focus of a web project. On the other hand, the domain ending also offers a readable and pronounceable alternative to classic top-level domains with high demand, making it a good option if an address name under .com is no longer available.
Advantages and disadvantages of a .io domain
The originally country-specific top-level domain .io has now found a place in the tech world and is also gaining popularity as a creative element for web projects beyond just IT and technology. Lastly, let’s explore the key advantages and disadvantages of using a domain with the .io TLD:
| Advantages of a .io domain | Disadvantages of a .io domain |
|---|---|
| ✓ High recognition value | ✗ Less accessible for people without an IT background |
| ✓ Many domain names are (still) available | ✗ May be seen as a sign of a weak brand |
| ✓ Well-suited for domain hacks | ✗ Relatively expensive |
| ✓ Google treats .io as a generic TLD | ✗ Revenue does not benefit the territory owner, unlike other ccTLDs |
| ✓ Shorter than alternatives like .com or .app |
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