Domain Name Maximum Length (253 chars) Regex for PHP

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 PHP. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

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

define('DOMAIN_NAME_MAXIMUM_LENGTH_253_CHARS_PATTERN', '/^(?=.{1,253}$)(?:[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?\.)*[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?$/');

function validate_domain_name_maximum_length_253_chars(string $input): bool {
    return (bool) preg_match(DOMAIN_NAME_MAXIMUM_LENGTH_253_CHARS_PATTERN, $input);
}

// Example
var_dump(validate_domain_name_maximum_length_253_chars("example.com")); // bool(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 PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. 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.