Punycode / Internationalized Domain Name Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching punycode / internationalized domain name, ported and verified for JavaScript. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// Punycode / Internationalized Domain Name
// ReDoS-safe | RegexVault — Web & Network > Domain

const punycodeInternationalizedDomainNameRegex = /^(?:(?:xn--[a-zA-Z0-9]{1,59}|[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?)?\.)*(?:xn--[a-zA-Z0-9]{1,59}|[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?)$/i;

function validatePunycodeInternationalizedDomainName(input: string): boolean {
  return punycodeInternationalizedDomainNameRegex.test(input);
}

// Example
console.log(validatePunycodeInternationalizedDomainName("xn--nxasmq6b.com")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Domain category and carries a ReDoS-safe certification. That matters for JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

IDN TLDs also use Punycode (e.g., .xn--p1ai for .рф). Always normalize and validate IDN using a dedicated library (e.g., idna in Python) rather than relying solely on regex.