Can domain name have two continuous hyphens

Question

I looked up couple of questions on SO, which seem to suggest that two continuous hyphens (e.g. my--website.com) are not allowed but when I search for same domain name on http://www.register.com/index.rcmx, it gladly accepts the name while rejects non valid domain names like my#website.com.
Validation for URL/Domain using Regex? (Rails)

score 13 · Accepted Answer · answered May 09 '13 at 18:15

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It's legal in a domain name, and required for internationalised domain names (IDNs) which when converted from Unicode to ASCII end up prefixed with xn--

answered May 09 '13 at 18:15

Alnitak

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This has rules which would allow double dashes: http://www.faqs.org/rfcs/rfc1035.html – Lee Meador May 09 '13 at 18:21
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RFC1035 is not the last word on legal domain names and host names - there's more in RFC 2181. – Alnitak May 09 '13 at 18:25

score 8 · Answer 2 · answered Mar 29 '16 at 12:32

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In general double hyphens are allowed. However, in your specific example, it should not be possible, because they may not occur on the third and fourth position except when writing IDN labels in their xn-- notation. See the following section from RFC 5891:

4.2.3.1. Hyphen Restrictions

The Unicode string MUST NOT contain "--" (two consecutive hyphens) in the third and fourth character positions and MUST NOT start or end with a "-" (hyphen).

answered Mar 29 '16 at 12:32

Michael

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Every third and fourth, or just the third and fourth? – Pacerier Jan 03 '20 at 12:15
Just the third and fourth character. – Jan Aagaard Jan 09 '20 at 08:26
And only for INTERNATIONALIZED DNS, e.g. http://xn--j1ail.xn--p1ai/ which is the ASCII version of http://кто.рф – abatishchev Oct 05 '20 at 22:01

dandwyer · Answer 3 · 2022-06-20T09:20:05.967

Some TLDs allow as many consecutive dashes as you want, others seem to have specific rules about their positioning.

This is a working website: l-------------------------------------------------------------l.tk (mirror)

The universal rules are:

Not in the 3rd and 4th position, except as part of an IDN
Not at the beginning or end

Nothing else can be counted on unless you thoroughly test each individual TLD.

score -1 · Answer 4 · answered May 08 '19 at 01:56

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It must be "allowed", regardless of the answers here, because https://hp--community.force.com exists. However, perhaps that's only okay because it's a subdomain of a registered domain, and not a registered domain in itself.

answered May 08 '19 at 01:56

Dan

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I'm quite sure the rules for subdomains are different - and less restrictive - than the ones for domain names. – Jan Aagaard Jan 09 '20 at 08:26

Can domain name have two continuous hyphens

4 Answers4

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