What does .io stand for? .io is the country code for British Indian Ocean Territory, but tech companies adopted it because "I/O" means input/output in programming. Reproof reports that 18% of Y Combinator companies now use .io[1]. The extension signals tech startup credibility to developers, VCs, and tech buyers, making it the go-to alternative when .com isn't available.
.io Domain Guide
Everything you need to know about .io domains
What is .io?
.io is the country code top-level domain (ccTLD) for British Indian Ocean Territory. Tech companies repurposed it because "I/O" means input/output in programming. Data from Reproof shows that only 42% of Y Combinator startups in the winter 2023 batch use a .com domain, down from over 90% in 2013[2]. This shift made .io the unofficial TLD for tech startups.
The first major companies to use .io did so out of necessity. Good .com names were taken. But the pattern stuck. Registry revenue for .io reached £31.6 million ($42.4 million) in 2024, according to Internet Computer Bureau filings[3]. Today, a .io domain signals "we're a tech company" to developers, investors, and technical audiences. The rise of .ai has created a natural competitor. Our .io vs .ai comparison breaks down when each extension makes sense.
Notable companies using .io include GitHub Pages (github.io), Linear, and hundreds of YC-backed startups. The extension has become shorthand for "this is a tech product."
Who Should Use .io?
SaaS Companies
.io tells potential customers you're a software product before they read a word of copy. B2B SaaS companies often find .io performs as well as .com with technical buyers who recognize the extension. Companies like Linear.app started on .io before acquiring premium .com domains. The .io carried them through early growth without hurting credibility. If your buyers are developers, product managers, or technical decision-makers, .io won't require explanation.
Developer Tools and APIs
APIs, SDKs, and developer platforms fit naturally under .io. GitHub's Pages service runs on github.io. Documentation sites, package registries, and CLI tools all use the extension. Your audience expects tech companies to use tech-signaling domains. Choosing .com when building developer infrastructure can actually seem out of touch. Socket.io, Repl.it, and hundreds of npm packages use .io because their users recognize it instantly.
Startups Seeking Investment
VCs recognize .io as the startup TLD. Research from Reproof found that .io is the second most popular TLD among YC-backed companies, with 2.3x more startups using .com than .io[2]. This gap has been narrowing every year since 2013. It won't hurt your fundraising, and it's often easier to find a memorable .io than .com. For a deeper look at how tech startups choose domain names, including TLD usage across YC batches, see our industry guide.
Open Source Projects
.io pairs naturally with GitHub repositories. Many open source projects use their GitHub org name with .io for documentation sites. It creates instant recognition for developers who spend their days on GitHub. The pattern works well: yourproject.io for docs, github.com/org/yourproject for code. Projects like Svelte.dev could have been Svelte.io (and many similar projects chose that path).
Who Should Avoid .io
B2C companies targeting non-technical audiences should think twice. If your customers are unlikely to know what .io means, you'll spend marketing dollars explaining your domain instead of your product. Local businesses, restaurants, and retail brands should stick with .com. The exception: if you're building a consumer app for a tech-savvy audience (productivity tools, finance apps for millennials), .io can still work.
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Pricing & Registration
.io domains typically cost $28-52/year through major registrars. Prices vary significantly. Registry wholesale prices have increased 25% since 2023, according to Cloudflare community discussions[4]. The Internet Computer Bureau, which controls the .io registry, sets wholesale prices that registrars then mark up.
Registration is straightforward with no special requirements. Anyone can register a .io domain. Domains register in 1-year increments and can be renewed for up to 10 years.
Premium .io domains (short words, common terms) can cost thousands. But .io's smaller registry of 1.6 million domains means better availability than .com's 160+ million. Generic two-word combinations often remain available at standard prices.
Registrar Price Comparison
Pricing data from registrar websites as of early 2025. Cloudflare sells at wholesale cost with no markup; others add their own margins.
| Registrar | Registration | Renewal | Notes |
|---|---|---|---|
| Porkbun | $28.12 | $51.80 | First-year discount, good support |
| Cloudflare | $45.00 | $45.00 | At-cost pricing, no markup |
| Namecheap | $32-45 | $45-49 | Frequent promotions |
| GoDaddy | $49+ | $59+ | Higher prices, watch renewal costs |
For long-term savings, Cloudflare's consistent at-cost pricing often beats first-year discounts that jump on renewal.
How .io Compares
| TLD | Best For | Price Range | Credibility |
|---|---|---|---|
| .io | Tech startups, dev tools | $30-60/year | High (in tech) |
| .com | Everything | $10-15/year | Highest |
| .ai | AI/ML companies | $50-100/year | High (in AI) |
| .dev | Developers, portfolios | $12-20/year | High (in dev) |
Email Deliverability on .io Domains
A common concern: will emails from your .io domain land in spam? The short answer is no, if you set up email properly.
In the early 2010s, some spam filters flagged unusual TLDs including .io. This reputation issue has largely resolved. Modern email filtering relies on sender reputation, authentication records, and content analysis rather than TLD alone. Litmus community discussions confirm that TLD choice has minimal impact on deliverability when authentication is configured correctly[5].
To ensure reliable delivery from a .io domain:
- Configure SPF, DKIM, and DMARC: These authentication protocols prove you control your domain
- Use a reputable email provider: Google Workspace, Microsoft 365, or a dedicated transactional service like Postmark
- Warm up new domains gradually: Don't send thousands of emails from a fresh domain
- Monitor sender reputation: Tools like Google Postmaster help you track deliverability
The TLD matters far less than your sending practices. Companies like Linear and Socket.io send millions of emails from .io domains without issues.
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Try DecideDomain FreeFAQ
What does .io stand for?
.io is technically the country code for British Indian Ocean Territory. Tech companies adopted it because "I/O" stands for input/output in programming. The double meaning made it popular with startups, developer tools, and SaaS companies.
Is .io good for SEO?
Google treats .io as a generic TLD, not a country-specific one. This means .io domains can rank globally without geographic restrictions. SEO performance depends on content quality, not the TLD itself.
Why is .io more expensive than .com?
.io costs $30-60/year compared to $10-15 for .com because the registry (Internet Computer Bureau) sets higher wholesale prices. The tech industry's demand for .io domains keeps prices elevated despite better availability than .com.
Should a startup use .io or .com?
Use .com if you can get a good name. If your preferred .com is taken or too expensive, .io signals tech credibility to investors and developers. For B2B tech companies, .io often performs as well as .com for brand recognition.
Will .io domains disappear due to BIOT sovereignty changes?
The British Indian Ocean Territory is being transferred to Mauritius, raising questions about .io's future. While this creates uncertainty, precedent suggests the TLD will continue. When .su (Soviet Union) and .yu (Yugoslavia) continued after those countries dissolved, registrations remained valid. The .io registry generates significant revenue, creating incentive to maintain operations. That said, risk-averse companies may want a .com backup.
Sources
- Register.domains .IO Domain Guide 2025: .io registration growth from 660,000 (2021) to 1.6+ million (2025)
- Reproof: The Slow Death of Dot Com: Y Combinator TLD usage analysis showing .io at 18% of startups, .com declining from 90%+ to 42%
- InternetX Global Domain Report 2025: Internet Computer Bureau revenue data for .io registry (£31.6M in 2024)
- Cloudflare Community: .IO Price Increase: Discussion of .io wholesale price increases and registrar pricing (2024)
- Litmus Community: Does Domain Extension Impact Deliverability?: Discussion confirming TLD has minimal impact on email deliverability when authentication is configured