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Asked: 2026-05-16T11:34:04+00:00

What are the valid characters of a hostname? This would be something like a

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What are the valid characters of a hostname? This would be something like a networked computer or a web domain.

To put it in context, I am writing a PC game which connects to a remote server; so I have a field for hostname and a field for port. Obviously the port is a number in the Short range, but I need to know what all the possible hostname characters are (and any other pattern that might be required – does a hostname need to start with a letter?).

Examples of hostname include localhost or google.com.

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  1. Editorial Team

    Checkout this wiki, specifically the section Restrictions on valid host names

    Hostnames are composed of series of labels concatenated with dots, as are all domain names. For example, "en.wikipedia.org" is a hostname. Each label must be between 1 and 63 characters long, and the entire hostname (including the delimiting dots but not a trailing dot) has a maximum of 253 ASCII characters.

    The Internet standards (Requests for Comments) for protocols mandate that component hostname labels may contain only the ASCII letters ‘a’ through ‘z’ (in a case-insensitive manner), the digits ‘0’ through ‘9’, and the hyphen (‘-‘). The original specification of hostnames in RFC 952, mandated that labels could not start with a digit or with a hyphen, and must not end with a hyphen. However, a subsequent specification (RFC 1123) permitted hostname labels to start with digits. No other symbols, punctuation characters, or white space are permitted.

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