JWT Decoder
Decode and inspect JSON Web Tokens (JWT) to view header, payload, and signature.
JWT Token
About JSON Web Tokens (JWT)
What is JWT? JSON Web Token (JWT) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. JWTs are compact, URL-safe, and self-contained tokens commonly used for authentication and information exchange.
Unlike session-based authentication, JWTs are stateless and contain all necessary information within the token itself, making them ideal for distributed systems and microservices architectures.
Common Use Cases:
• User Authentication: Replace session cookies in web applications
• Single Sign-On (SSO): Enable seamless login across multiple applications
• API Authorization: Secure RESTful API endpoints
• Mobile Apps: Authenticate users in mobile applications
• Microservices: Pass user context between services
• Information Exchange: Securely transmit data between parties
JWT Structure
Three Parts (separated by dots):
1. Header (Algorithm & Token Type):
Contains metadata about the token, including the signing algorithm (e.g., HS256, RS256) and token type (JWT).
2. Payload (Claims):
Contains the claims - statements about an entity (typically the user) and additional data. Claims can be registered, public, or private.
3. Signature (Verification):
Created by encoding the header and payload with a secret key and the specified algorithm. Used to verify the token's integrity and authenticity.
JWT Token Example:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9
.
eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ
.
SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
Header
Payload
Signature
Standard JWT Claims:
• iss (Issuer): Who issued the token
• sub (Subject): Who the token is about (usually user ID)
• aud (Audience): Who should use the token
• exp (Expiration): When the token expires (Unix timestamp)
• nbf (Not Before): When the token becomes valid
• iat (Issued At): When the token was created
• jti (JWT ID): Unique identifier for the token
Security Best Practices:
• Never store sensitive data in JWT payload (it's only encoded, not encrypted)
• Use HTTPS to prevent token interception
• Set appropriate expiration times (short-lived tokens are more secure)
• Use strong secrets for HMAC algorithms (HS256, HS384, HS512)
• Consider using asymmetric algorithms (RS256, ES256) for better security
• Implement proper token revocation mechanisms when needed
Tool Features:
• Decode and display all three JWT parts in readable format
• Show token expiration and issued times in human-readable format
• Validate token structure and detect malformed tokens
• Copy individual parts (header, payload, signature) to clipboard
• Client-side processing - tokens never leave your browser
📚 Learn More:
• Read our comprehensive Understanding JWT Tokens Guide
• Learn about OAuth 2.0 Authentication
• Explore Base64 Encoder/Decoder for JWT payload encoding
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