🔍Regex Recipes

Domain Name Validation

Validate domain names with support for subdomains and international domains (with punycode note).

Pattern

^(?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]$

Explanation

Validates domain names including subdomains. Labels can be 1-63 characters. Note: International domains must be punycode-encoded.

Examples

Simple domain

Input

example.com

Output

✓ Match

With subdomain

Input

mail.example.com

Output

✓ Match

Multiple subdomains

Input

api.staging.example.com

Output

✓ Match

Invalid - hyphen at start

Input

-example.com

Output

✗ No match

Invalid - no TLD

Input

example

Output

✗ No match

Code Examples

JavaScript

const domainRegex = /^(?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]$/i;

// Validate domain
const isValid = domainRegex.test('example.com'.toLowerCase());

// For international domains, use punycode
const punycode = require('punycode/');
const encoded = punycode.toASCII('münchen.de'); // 'xn--mnchen-3ya.de'

Try it Now

Open in Regex Tester

💡 Tips

Convert to lowercase before validation
Use punycode library for international domains
Each label (part between dots) max 63 chars
Total domain name max 253 chars

⚠️ Common Pitfalls

International domain names (IDN) need punycode conversion
Does not validate if domain actually exists
TLD validation is basic (any 2+ letter combination)
Case-insensitive flag recommended