Hostname (Single Label) Regex Pattern
Validates a single DNS hostname label (no dots, 1-63 characters).
Pattern
^[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?$Tested examples
localhostmy-serverweb01-invalidhost.nametoolooooooooooooooooooooooooooooooooooooooooooooooooooooooooooongTest it live
Live Regex TesterJS
0 matches/
/g
localhost my-server web01
Use it in your language
Use it in
// JavaScript / Node.js
const regex = /^[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?$/;
const value = "localhost";
const isMatch = regex.test(value);
console.log(isMatch); // true / false
// Extract all matches
const matches = value.match(/^[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?$/g) || [];Tags
Frequently asked questions
How do I use the Hostname (Single Label) regex pattern in JavaScript?
Wrap the pattern in slashes: const re = /^[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?$/; — then call re.test(value) to check a single value, or value.match(re) to find matches. The "Use it in" snippets above give you the exact code for 9 languages.
Is this hostname (single label) regex production-ready?
Yes — every pattern in the library is tested against valid and invalid examples. Still, regex is one layer in a defense-in-depth strategy: pair it with server-side validation (e.g. Luhn for credit cards, mod-97 for IBAN, real DNS lookup for emails) for critical inputs.
Why does my pattern fail in another language?
Different regex engines (PCRE, Java, Python, Go's RE2) support slightly different syntax. The most common gotchas: lookbehinds (not in RE2), named groups syntax, and how backslashes need to be escaped inside string literals. The code snippets above already escape correctly for each language.
Can I edit this pattern and test it live?
Yes — use the live tester above. Type your test string and toggle flags (g, i, m, s, u, y) to see matches highlighted instantly, including capture groups.
Related patterns
See all Network →Network
MAC Address (Colon Format)
Validates MAC address in colon-separated format (AA:BB:CC:DD:EE:FF)
NetworkIPv4 Address
Validates IPv4 addresses (0.0.0.0 - 255.255.255.255).
NetworkIPv6 Address
Validates full and compressed IPv6 addresses.
NetworkFQDN (Fully Qualified Domain Name)
Validates fully qualified domain names (hostname.domain.tld).
NetworkIPv4 with CIDR Notation
Validates IPv4 addresses with CIDR notation (e.g., 192.168.1.0/24).
NetworkPort Number
Validates port numbers (1-65535).
Browse the full library — 250 tested regex patterns across 16 categories.