Domain Name Maximum Length (253 chars) Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching domain name maximum length (253 chars), 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

// Domain Name Maximum Length (253 chars)
// ReDoS-safe | RegexVault — Web & Network > Domain

const domainNameMaximumLength253CharsRegex = /^(?=.{1,253}$)(?:[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?\.)*[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?$/i;

function validateDomainNameMaximumLength253Chars(input: string): boolean {
  return domainNameMaximumLength253CharsRegex.test(input);
}

// Example
console.log(validateDomainNameMaximumLength253Chars("example.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

The lookahead (?=.{1,253}$) enforces the 253-character DNS limit. This is especially important for domains constructed programmatically. Go's RE2 does not support lookaheads — perform the length check separately in Go.