JSON Web Token (JWT) Regex for JavaScript

What this pattern does

This page provides a well-structured, multi-part regular expression for matching json web token (jwt), 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

// JSON Web Token (JWT)
// ReDoS-safe | RegexVault — Web & Network > Misc

const jsonWebTokenJwtRegex = /^[A-Za-z0-9\-_]+\.[A-Za-z0-9\-_]+\.[A-Za-z0-9\-_]*$/;

function validateJsonWebTokenJwt(input: string): boolean {
  return jsonWebTokenJwtRegex.test(input);
}

// Example
console.log(validateJsonWebTokenJwt("eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Misc 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 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.