JWT.io

Essential online tool for decoding, verifying, and generating JSON Web Tokens (JWT). JWT.io is the go-to resource for understanding and debugging JWTs used in authentication and authorization.

Features

JWT Debugger

• Decode & Verify: Instantly decode JWT tokens to see header, payload, and signature
• Visual Editor: Edit JWT claims in real-time with live encoding
• Signature Verification: Verify token signatures with your secret or public key
• Algorithm Support: HS256, HS384, HS512, RS256, RS384, RS512, ES256, ES384, ES512, PS256, PS384, PS512
• Copy-Paste Interface: Simple paste-and-decode workflow

Educational Resources

• JWT Introduction: Clear explanation of what JWTs are and how they work
• Use Cases: When and why to use JWTs
• Best Practices: Security recommendations and common pitfalls
• Libraries: Comprehensive list of JWT libraries for every language

How JWTs Work

A JWT consists of three parts:

1. Header: Algorithm and token type
2. Payload: Claims (user data, expiration, etc.)
3. Signature: Verification signature

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.
eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.
SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

Common Use Cases

Authentication

• User login tokens
• Single Sign-On (SSO)
• Session management
• Mobile app authentication

Authorization

• Role-based access control
• Permission verification
• API access tokens
• Microservices communication

Information Exchange

• Secure data transmission
• Stateless sessions
• Cross-domain authentication
• Third-party integrations

Security Best Practices

• Use HTTPS: Always transmit JWTs over secure connections
• Short Expiration: Set reasonable exp claims (15min-1hr)
• Validate Everything: Always verify signature and claims
• Strong Secrets: Use cryptographically strong signing keys
• Don't Store Sensitive Data: JWTs are encoded, not encrypted
• Implement Refresh Tokens: For long-lived sessions
• Blacklist When Needed: Have a revocation strategy

Libraries by Language

.NET

• System.IdentityModel.Tokens.Jwt
• jose-jwt
• JWT.NET

JavaScript/Node.js

• jsonwebtoken
• jose
• node-jsonwebtoken

Python

• PyJWT
• python-jose
• authlib

Java

• java-jwt
• jjwt
• jose4j

Debugging Workflow

1. Copy JWT from your application
2. Paste into JWT.io debugger
3. View decoded header and payload
4. Enter your secret/public key
5. Verify signature validity
6. Check expiration and claims

Best For

• Debugging authentication issues
• Understanding JWT structure
• Learning about token-based auth
• Verifying token signatures
• Testing JWT implementations
• Educational purposes

JWT.io is an invaluable tool for any developer working with modern authentication systems, making complex JWT debugging simple and accessible.