JSON Web Token (JWT) — Structure Validation Regex for PHP

What this pattern does

This page provides a well-structured, multi-part regular expression for matching json web token (jwt) — structure validation, ported and verified for PHP. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. 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) — Structure Validation
// ReDoS-safe | RegexVault — Security > API Keys & Tokens

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

function validate_json_web_token_jwt_structure_validation(string $input): bool {
    return (bool) preg_match(JSON_WEB_TOKEN_JWT_STRUCTURE_VALIDATION_PATTERN, $input);
}

// Example
var_dump(validate_json_web_token_jwt_structure_validation("eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Security > API Keys & Tokens 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

Structure only — does not validate header algorithm, payload claims, expiry, or signature. Three segments: header (base64url) + payload (base64url) + signature (base64url, may be empty for 'none' algorithm — always reject 'none'). Capture groups: 1=header, 2=payload, 3=signature.