JSON Web Token (JWT) Regex for PHP

What this pattern does

This page provides a well-structured, multi-part regular expression for matching json web token (jwt), 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
// JSON Web Token (JWT)
// ReDoS-checked | RegexVault — Web & Network > Misc

define('JSON_WEB_TOKEN_JWT_PATTERN', '/^[A-Za-z0-9\-_]+\.[A-Za-z0-9\-_]+\.[A-Za-z0-9\-_]*$/');

function validate_json_web_token_jwt(string $input): bool {
    return (bool) preg_match(JSON_WEB_TOKEN_JWT_PATTERN, $input);
}

// Example
var_dump(validate_json_web_token_jwt("eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Misc category and has been checked for ReDoS risk. 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 signature section may be empty for unsigned tokens (alg: none). NEVER use alg: none in production — always validate algorithm. This regex validates structure only, not cryptographic validity.