Letters, numbers and hyphens are the safe default
A standard domain label can use letters a to z, numbers 0 to 9 and hyphens, but it cannot contain spaces or ordinary punctuation
A hyphen cannot normally be the first or last character. Internationalised domain names can display supported non-ASCII scripts, but the registry converts them to a technical ASCII form and each extension sets its own permitted characters and length rules.
Which domain-name examples are valid?
| Example label | Normally valid? | Reason |
|---|---|---|
| example | Yes | Uses letters only |
| example24 | Yes | Letters and digits are permitted |
| my-example | Yes | The hyphen is inside the label |
| -example | No | A normal registered label cannot start with a hyphen |
| example- | No | A normal registered label cannot end with a hyphen |
| my example | No | Spaces are not domain-label characters |
| sales@example | No | @ separates the local part from the domain in an email address; it is not part of the domain |
| example! | No | Ordinary punctuation such as !, &, / and ? is not allowed in a registered ASCII label |
How long can a domain name be?
One DNS label
The technical limit for a single ASCII DNS label is 63 octets. The label is the part between dots, such as example in example.co.uk.
The complete domain
The full name has a larger DNS wire-format limit and is commonly treated as no more than 253 visible characters without a final root dot.
The registry minimum
There is no universal three-character minimum for every extension. A registry can set its own minimum and reserve otherwise valid short names.
Internationalised names
The converted ASCII form must fit the DNS limit, so the number of visible Unicode characters is not the only length test.
For customers, the practical target is much shorter. A concise name is easier to type, fit on printed material, read over the telephone and use in an email address.
Can a domain use accented, Japanese or other international characters?
Some extensions support internationalised domain names, known as IDNs. The visible Unicode name is converted into an ASCII-compatible form called Punycode, which begins with xn--. Browsers can display the readable version when their safety and language rules permit it.
Extension support varies
A script accepted by one registry may be unavailable under another. Search through the intended extension and check its current IDN table.
Software support varies
Browsers, forms, email apps and older systems can display or process the converted name differently. Test the full customer journey.
Lookalike risk matters
Characters from different scripts can look similar. Avoid a name that customers may mistake for a different brand or website.
Register the practical companion
Where appropriate, also secure an easy ASCII version and redirect it to the preferred site so customers have a reliable fallback.
ICANN explains the technical and policy background in its internationalised domain name resource.
Why do email addresses appear to allow more characters?
An email address contains two different parts:
| Part | Example | Rule |
|---|---|---|
| Local part | sales in sales@example.uk | The mailbox system decides which supported characters can appear before @ |
| Separator | @ | Separates the mailbox local part from the domain and cannot be inside the registered domain |
| Domain | example.uk | Must follow the DNS and registry rules for its labels and extension |
What should you check beyond technical validity?
- 1Say it aloud
Ask whether a customer can hear the name once and type it correctly without extra explanation.
- 2Check the hyphens and digits
Decide whether people will know to type a hyphen, or whether a spoken number is written as a digit or word.
- 3Review neighbouring names
Check likely misspellings, the matching .co.uk, .uk and .com, and any confusingly similar established business.
- 4Check rights and restrictions
Availability does not grant rights to another party’s name, trade mark or reserved registry term.
- 5Test the full address
Place the name after www and in sample email addresses to see whether it remains clear and manageable.
- 6Search the exact extension
The registry’s availability response is the final practical character and reservation test for that order.
Domain character questions
Can a domain name contain a space?
No. A normal registered domain label cannot contain spaces. Use a hyphen if separation is essential, or combine the words.
Can a domain name contain an underscore?
Not as an ordinary website hostname label registered for people to use. DNS uses underscore-prefixed labels for technical records such as _dmarc and _sip, which are different from the registrable domain name.
Can a domain start or end with a hyphen?
A normal ASCII registration cannot. Internationalised names use a reserved converted prefix, so do not manually treat xn-- as an ordinary naming trick.
Can I use an ampersand or apostrophe?
Not in a standard ASCII domain label. Replace the symbol with a word, omit it or choose another clear variation.
Are one-character and two-character names allowed?
The technical DNS format can represent them, but the registry decides whether short labels can be newly registered and many are reserved or already taken. Search the exact extension.
Does the extension count toward the 63-character label limit?
No. The 63-octet limit applies to each individual label between dots. The whole domain also has its own larger DNS limit.
Valid is not always memorable
Use the simplest permitted name that customers can read, type and trust
Search the exact extension to confirm its current length, character, IDN and reserved-name rules before ordering.