Gray-wolf Tools Logo Gray-wolf Tools
Decorative header image for JWT Generator Tool: Create Secure JSON Web Tokens

JWT Generator Tool: Create Secure JSON Web Tokens

Generate secure JWT tokens with custom claims, headers, and signing algorithms. Perfect for testing, development, and understanding token structure.

By Gray-wolf Tools Team • Content Team
Updated 11/3/2025 • ~800 words
security jwt token-generation authentication cryptography

Executive Summary

The JWT Generator Tool is a comprehensive solution for creating JSON Web Tokens (JWTs) with custom claims, headers, and signing algorithms. Whether you’re developing authentication systems, testing API integrations, or learning about token-based security, this tool provides an intuitive interface for generating secure, properly formatted JWTs. With support for multiple signing algorithms (HS256, HS384, HS512, RS256, RS384, RS512) and customizable payload structures, developers can create tokens that match their exact specifications without writing code.

JSON Web Tokens have become the industry standard for secure information transmission between parties. This tool eliminates the complexity of manual JWT creation by providing a user-friendly interface that handles encoding, signing, and formatting automatically. Whether you’re generating tokens for OAuth 2.0 flows, session management, or API authentication, the JWT Generator Tool ensures your tokens are cryptographically sound and standards-compliant.

Feature Tour

Algorithm Selection

Choose from industry-standard signing algorithms including HMAC-based (HS256, HS384, HS512) and RSA-based (RS256, RS384, RS512) methods. Each algorithm offers different security characteristics:

  • HMAC Algorithms (HS256/384/512): Symmetric key signing using shared secrets, ideal for server-to-server communication
  • RSA Algorithms (RS256/384/512): Asymmetric key signing using public/private key pairs, perfect for distributed systems

Custom Header Configuration

Define JWT headers with precision, including algorithm type (alg), token type (typ), and custom header claims. The tool automatically validates header structure and ensures compliance with RFC 7519 specifications.

Flexible Payload Builder

Create complex payload structures with nested objects, arrays, and multiple claim types. Support for standard claims includes:

  • iss (Issuer): Identifies the token creator
  • sub (Subject): Identifies the token subject
  • aud (Audience): Identifies intended recipients
  • exp (Expiration): Sets token expiration timestamp
  • nbf (Not Before): Defines when token becomes valid
  • iat (Issued At): Records token creation time
  • jti (JWT ID): Provides unique token identifier

Signature Generation

Automatically generate cryptographic signatures using your chosen algorithm and secret key. The tool handles base64url encoding, signature computation, and final token assembly, producing ready-to-use JWT tokens.

Token Preview

View your generated token in real-time with syntax highlighting and structure breakdown. See the encoded header, payload, and signature components separately before combining them into the final token.

Export Options

Copy generated tokens to clipboard, download as text files, or export with metadata including generation timestamp, algorithm used, and expiration details.

Usage Scenarios

API Development and Testing

Generate test tokens for API endpoint authentication during development. Create tokens with specific user roles, permissions, or scopes to test authorization logic without setting up full authentication infrastructure. Use the JWT Inspector Tool to verify your generated tokens are correctly formatted.

OAuth 2.0 Implementation

Create JWT tokens for OAuth 2.0 flows including authorization grants, refresh tokens, and access tokens. Customize claims to match your OAuth provider requirements and test token-based authentication workflows.

Microservices Authentication

Generate service-to-service authentication tokens for microservices architectures. Create tokens with specific service identifiers, roles, and permissions to secure internal API communications.

Session Management

Build JWT-based session tokens containing user identity, session metadata, and expiration times. Replace traditional session cookies with stateless JWT tokens for scalable authentication.

Educational Purposes

Learn JWT structure and cryptographic signing by experimenting with different algorithms, payloads, and secrets. Understand how header, payload, and signature components combine to create secure tokens.

Code Examples

Generating Basic JWT Token

// Using the generated token in JavaScript
const token = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c";

// Add to HTTP request headers
fetch('https://api.example.com/protected', {
  headers: {
    'Authorization': `Bearer ${token}`
  }
})
.then(response => response.json())
.then(data => console.log(data));

Token with Custom Claims

{
  "header": {
    "alg": "HS256",
    "typ": "JWT"
  },
  "payload": {
    "sub": "user123",
    "name": "Alice Johnson",
    "email": "alice@example.com",
    "role": "admin",
    "permissions": ["read", "write", "delete"],
    "iat": 1699000000,
    "exp": 1699086400
  }
}

Using with Express.js Middleware

// Validate generated token in Express.js
const jwt = require('jsonwebtoken');

function authenticateToken(req, res, next) {
  const token = req.headers['authorization']?.split(' ')[1];
  
  if (!token) {
    return res.status(401).json({ error: 'Token required' });
  }
  
  jwt.verify(token, process.env.JWT_SECRET, (err, user) => {
    if (err) {
      return res.status(403).json({ error: 'Invalid token' });
    }
    req.user = user;
    next();
  });
}

app.get('/api/protected', authenticateToken, (req, res) => {
  res.json({ message: 'Access granted', user: req.user });
});

Python Token Verification

import jwt
from datetime import datetime

# Verify generated token
token = "your-generated-token-here"
secret = "your-secret-key"

try:
    decoded = jwt.decode(token, secret, algorithms=["HS256"])
    print(f"Token valid. Subject: {decoded['sub']}")
    
    # Check expiration
    if decoded['exp'] < datetime.now().timestamp():
        print("Token expired!")
    else:
        print("Token is active")
        
except jwt.InvalidSignatureError:
    print("Invalid signature")
except jwt.ExpiredSignatureError:
    print("Token has expired")
except jwt.DecodeError:
    print("Token decode error")

Troubleshooting

Token Signature Verification Fails

Problem: Generated token fails signature verification in your application.

Solutions:

  • Ensure the secret key used for generation matches the verification key exactly (case-sensitive)
  • Verify algorithm selection matches between generation and verification (HS256 vs RS256)
  • Check that the token hasn’t been modified after generation
  • For RSA algorithms, confirm you’re using the correct public/private key pair

Token Rejected as Expired

Problem: Token shows as expired immediately after generation.

Solutions:

  • Check system time synchronization between generation and verification servers
  • Verify exp claim is set to future timestamp (Unix epoch format)
  • Add buffer time using nbf claim to account for clock skew
  • Use the Password Generator to create strong secrets for longer-lived tokens

Invalid Token Format Error

Problem: Generated token produces format errors when decoded.

Solutions:

  • Ensure payload contains valid JSON (no trailing commas, proper quoting)
  • Verify all claims use correct data types (strings, numbers, arrays)
  • Check for special characters that need escaping in claim values
  • Validate the token has three dot-separated segments (header.payload.signature)

Algorithm Not Supported Error

Problem: Verification library doesn’t recognize the signing algorithm.

Solutions:

  • Confirm your JWT library supports the selected algorithm (some don’t support RS algorithms)
  • Update JWT library to latest version for broader algorithm support
  • Use HS256 as the most widely supported algorithm for testing
  • Check library documentation for required dependencies (OpenSSL for RSA)

Accessibility Considerations

The JWT Generator Tool includes keyboard navigation support, screen reader compatibility, high-contrast mode for visibility, and clear error messages. All interactive elements are accessible via Tab navigation, and ARIA labels provide context for assistive technologies.

Frequently Asked Questions

What’s the difference between HS256 and RS256 algorithms?

HS256 uses symmetric HMAC signing with a shared secret key, meaning the same key is used for both signing and verification. RS256 uses asymmetric RSA signing with a public/private key pair, where tokens are signed with the private key and verified with the public key. Use HS256 for server-to-server communication where you control both parties, and RS256 when tokens need verification by multiple independent parties.

How do I choose an appropriate expiration time?

Set expiration based on token purpose: short-lived access tokens (15 minutes to 1 hour) for API access, longer refresh tokens (days to weeks) for obtaining new access tokens, and session tokens based on user activity patterns. Always use the shortest practical lifetime to minimize security risks from token compromise. Combine with the File Text Hasher for additional security layers.

Can I generate tokens without an expiration claim?

Yes, the exp claim is optional in JWT specifications, but it’s strongly recommended for security. Tokens without expiration remain valid indefinitely unless manually revoked, creating security vulnerabilities. Always include exp claims for production tokens, reserving non-expiring tokens only for testing or specific use cases with alternative revocation mechanisms.

What secret key length should I use for HS256?

For HS256, use secrets at least 256 bits (32 bytes) long to match the algorithm’s output size. Longer secrets provide stronger security. Generate cryptographically random secrets using secure random number generators, not passwords or predictable strings. Never hardcode secrets in source code; use environment variables or secret management services.

How do I handle token refresh?

Implement refresh token patterns by generating two tokens: a short-lived access token for API requests and a long-lived refresh token for obtaining new access tokens. When the access token expires, send the refresh token to a dedicated endpoint that validates it and issues a new access token. This minimizes exposure while maintaining user sessions.

Can I include sensitive data in JWT payloads?

JWT payloads are base64url encoded but not encrypted—anyone with the token can decode and read the payload. Never include passwords, credit card numbers, or other sensitive data in JWT payloads. Include only necessary identifiers and claims, keeping sensitive data in secure backend storage referenced by token claims.

What’s the maximum token size?

While JWT has no strict size limit, keep tokens under 8KB to avoid HTTP header size limits in web servers and browsers. Large tokens increase bandwidth usage and can cause issues with URL length limits when passed as query parameters. Minimize payload size by using short claim names and avoiding unnecessary data.

How do I revoke a JWT token?

JWTs are stateless and cannot be revoked inherently. Implement revocation through: (1) short expiration times requiring frequent token renewal, (2) maintaining a blacklist/deny-list of revoked token IDs checked during verification, (3) versioning tokens and incrementing version numbers when revoking all user tokens, or (4) using refresh token rotation with server-side tracking.

References