Regex for Domain Name — Pattern Explained with Examples

Domain name validation is essential for URL processing, email validation, and network configuration. This pattern checks that a string follows DNS label conventions: alphanumeric characters and hyphens, no leading or trailing hyphens, and a valid top-level domain.

The Pattern

/^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z]{2,}$/

Pattern Breakdown

Matches

• example.com
• sub.domain.com
• my-site.io
• google.co.uk
• api.v1.example.org

Does NOT Match

• -example.com
• example..com
• .com
• example.c (too short TLD)
• exam ple.com
• http://example.com

Language Examples

JavaScript

const domainRegex = /^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z]{2,}$/;
console.log(domainRegex.test('example.com')); // true
console.log(domainRegex.test('-example.com')); // false

Python

import re
pattern = r'^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z]{2,}$'
print(bool(re.match(pattern, 'example.com')))  # True
print(bool(re.match(pattern, '-example.com')))  # False

Common Pitfalls

• TLD minimum length is 2, but many new gTLDs are longer (e.g., .international, .technology) — the {2,} quantifier handles this correctly
• Internationalized domain names (IDN) use punycode (xn--) prefixes which this ASCII-only pattern does not match
• The full domain must be 253 characters or fewer, and each label maxes out at 63 characters — this pattern enforces label length but not total length
• Do not include protocol (http://), port numbers, or path segments in domain validation — use a URL regex for those
• Trailing dots (FQDN notation) are technically valid in DNS but rejected by this pattern

Real-World Use Cases

• Email validation — the domain portion after @ must be a valid domain name
• Link sanitization — extract and verify domain names from user-submitted URLs
• DNS configuration tools — validate domain entries before making DNS API calls

FAQ

Related Patterns

Regex for Email Regex for URL