JWT Builder

JWT Builder is a browser-based tool that allows users to create JWTs(JSON Web Tokens) by specifying standard claims, adding custom claims, and signing tokens using HMAC-SHA256 (HS256) algorithm. The tool provides an intuitive interface for JWT generation with real-time validation and error handling.

Need to parse an existing token? Use the JWT Parser and validator!

JWT Builder Features:

• Support for all standard JWT claims:
• `iss` (Issuer)
• `sub` (Subject)
• `aud` (Audience)
• `exp` (Expiration Time)
• `nbf` (Not Before)
• `iat` (Issued At)
• `jti` (JWT ID)
• Custom claim support with dynamic field addition
• Flexible datetime input handling:
• Accepts both ISO 8601 datetime strings (e.g., “2025-12-31T23:59:59Z”)
• Supports UNIX timestamps
• Automatic timestamp conversion and validation
• HMAC-SHA256 (HS256) signature generation
• Copy-to-clipboard functionality
• Real-time error handling and feedback
• Default values for quick testing
  

Usage Example:

1. Fill in the standard claims:
   • Issuer: The entity issuing the token (e.g., “my-app”)
   • Subject: The subject of the token (e.g., “user123”)
   • Audience: The intended recipient (e.g., “my-api”)
   • Expiration: When the token expires (e.g., “2025-12-31T23:59:59Z”)
   • Other standard claims as needed
2. Add custom claims (if required):
   • Click “Add Claim” button
   • Enter claim name and value
   • Add multiple custom claims as needed
3. Enter your signature key:
   • Provide a secure secret key for signing the JWT
4. Generate the JWT:
   • Click “Build JWT” button
   • The generated JWT will appear in the output section
5. Copy the token:
   • Click “Copy JWT” button to copy the token to the clipboard
   • Use the token in your application

Technology Stack

• Frontend: Pure HTML, CSS, and JavaScript
• Cryptography: Web Crypto API
  • HMAC-SHA256 for token signing
  • Secure key handling using SubtleCrypto
• Encoding:
  • Base64URL encoding for JWT components
  • UTF-8 encoding for string handling
• Input Processing:
  • DateTime parsing and validation
  • JSON structure validation
  • Chunk-based string processing for large tokens

Built with the Help of Claude 3.5 Sonnet LLM

Security Considerations

• All cryptographic operations are performed using the standardized Web Crypto API
• No external dependencies are required for JWT generation
• Client-side only – no data is sent to any server
• The signature key is never stored or transmitted

Browser Compatibility

Compatible with modern browsers that support:

• Web Crypto API
• TextEncoder API
• Clipboard API
• ES6+ JavaScript features