Decode & Verify JSON Web Tokens
JWT.app is the most trusted online tool for decoding, verifying and generating JSON Web Tokens. Used by developers worldwide to debug and understand JWT authentication in their applications.
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Understanding JSON Web Tokens
JSON Web Tokens are an open, industry-standard RFC 7519 method for representing claims securely between two parties. JWT.app allows you to decode, verify and generate JWT.
Header
Contains metadata about the type of token and the cryptographic algorithms used to secure its contents.
{
"alg": "HS256",
"typ": "JWT"
}Payload
Contains a set of claims. Claims are statements about an entity (typically, the user) and additional data.
{
"sub": "1234567890",
"name": "John Doe",
"admin": true
}Signature
Securely validates the token. The signature is calculated by encoding the header and payload using Base64url Encoding.
HMACSHA256(
base64UrlEncode(header) + "." +
base64UrlEncode(payload),
secret)Powerful JWT Tools
Decode JWT Tokens
Instantly decode JWT tokens to inspect their contents, view claims, and understand their structure without any setup.
Try Decoder âVerify Signatures
Validate JWT signatures using various algorithms to ensure tokens haven't been tampered with and are authentic.
Verify Now âLearn Best Practices
Master JWT implementation with our comprehensive guides, security best practices, and real-world examples.
Read Articles âHow JWT Authentication Works
Understanding the JWT authentication flow is crucial for implementing secure authentication in modern applications.
User Authentication
User provides credentials to the authentication server, which validates them against the user database.
Token Generation
Server creates a JWT containing user information and signs it with a secret key or private key.
Token Storage
Client receives and stores the JWT securely, typically in memory, localStorage, or as an HTTP-only cookie.
Authenticated Requests
Client includes the JWT in the Authorization header for subsequent requests, server validates and processes them.
Where to Use JSON Web Tokens
JWTs are versatile and can be used in various scenarios for authentication and information exchange.
API Authentication
Secure your RESTful APIs and GraphQL endpoints with stateless JWT authentication for better scalability.
Mobile Applications
Perfect for native iOS and Android apps where traditional session management is impractical.
Microservices
Enable secure service-to-service communication in distributed architectures without centralized sessions.
Single Sign-On
Implement SSO across multiple domains and applications with JWT for seamless user experience.
Frequently Asked Questions
What is a JWT?
JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed.
What is the structure of a JWT?
A JWT consists of three parts separated by dots: Header, Payload, and Signature. The header typically contains the token type and the signing algorithm. The payload contains the claims or the JWT's data. The signature is used to verify that the sender of the JWT is who it says it is.
When should I use JWTs?
JWTs are commonly used for authorization and information exchange. They're great for Single Sign-On (SSO), API authentication, and secure data transmission between parties.
Are JWTs secure?
JWTs can be secure when implemented correctly. They should be transmitted over HTTPS, use strong signing algorithms, have short expiration times, and sensitive data should be encrypted or kept out of the payload.
JWT vs. session cookies?
JWTs are stateless and can contain user data, making them suitable for distributed systems. Session cookies require server-side storage but can be revoked immediately. The choice depends on your specific requirements for security, scalability, and functionality.
How do I revoke a JWT?
JWTs cannot be revoked before expiration by design. Common solutions include maintaining a token blacklist, using short expiration times with refresh tokens, or implementing token versioning in your user database.
What is the maximum size of a JWT?
While JWTs have no official size limit, practical constraints exist. Most web servers limit header sizes to 4-8KB. Keep your JWTs under 4KB by minimizing claims and using efficient signing algorithms.
Which signing algorithm should I use?
For symmetric encryption, use HS256. For asymmetric, RS256 offers wide compatibility while ES256 provides better performance. In 2025, EdDSA is recommended for new applications due to its security and performance benefits.
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