JWT Decoder
Decode and inspect JSON Web Tokens (JWT) instantly. View header, payload, and token information without storing your data.
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How to Use the JWT Decoder
Learn how to decode JSON Web Tokens in seconds with our step-by-step guide
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Copy the JWT token from your application, API response, or authentication system. Include the full token with all three parts.
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Instantly see the decoded header, payload, and token information including expiration status and claims.
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What is a JSON Web Token (JWT)?
Understanding the fundamentals of JWT tokens and how they work in modern web applications
JWT Structure Explained
A JSON Web Token (JWT) is a compact, URL-safe token format that represents claims between two parties. JWTs are commonly used for authentication and secure information transmission in web applications.
Every JWT consists of three parts separated by dots: Header.Payload.Signature. Each part is Base64URL encoded, making it safe for transmission over HTTP.
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
JWT Components
Header
Contains token type (JWT) and signing algorithm (HS256, RS256, etc.)
Payload
Contains claims (user data, permissions, expiration time, etc.)
Signature
Verifies token integrity and authenticity using secret key
Understanding JWT Claims
JWT claims are pieces of information asserted about a subject. Learn about standard and custom claims.
Standard Claims
iss (Issuer)
Identifies who issued the token
"iss": "https://auth.example.com"sub (Subject)
Identifies the token subject (usually user ID)
"sub": "user123"aud (Audience)
Identifies token recipients
"aud": ["api.example.com"]exp (Expiration)
When the token expires (Unix timestamp)
"exp": 1693526400iat (Issued At)
When the token was issued
"iat": 1693440000nbf (Not Before)
Token not valid before this time
"nbf": 1693440000Custom Claims
User Information
Store user profile data
"name": "John Doe" "email": "john@example.com"Permissions & Roles
Define user access levels
"roles": ["admin", "user"] "permissions": ["read", "write"]Application Data
Store app-specific information
"tenant_id": "company123" "session_id": "sess_abc123"Best Practice
Keep JWTs small by avoiding sensitive data. Store only essential claims needed for authorization.
JWT Signing Algorithms
Learn about different JWT signing algorithms and when to use each one for maximum security
HMAC (Symmetric)
Uses a shared secret key for both signing and verification. Fast and simple, perfect for single-application scenarios.
Use Cases:
- • Single-service authentication
- • Internal API tokens
- • Session management
RSA (Asymmetric)
Uses public/private key pairs. Private key signs, public key verifies. Ideal for distributed systems and microservices.
Use Cases:
- • Microservices architecture
- • Third-party integrations
- • OpenID Connect
ECDSA (Elliptic Curve)
Elliptic Curve Digital Signature Algorithm. Provides same security as RSA with smaller key sizes and better performance.
Use Cases:
- • Mobile applications
- • IoT devices
- • High-performance systems
JWT Security Best Practices
Follow these essential security guidelines to implement JWT tokens safely in your applications
Use Strong Secrets
Use cryptographically secure random strings of at least 256 bits for HMAC algorithms. Store secrets securely in environment variables.
Never hardcode secrets in your source code!
Set Short Expiration
Use short expiration times (15-60 minutes) for access tokens. Implement refresh tokens for longer sessions without compromising security.
Recommended: 15 minutes for access tokens
HTTPS Only
Always transmit JWTs over HTTPS to prevent interception. Use secure cookie flags when storing tokens in cookies.
TLS 1.2+ required for production
Validate Everything
Always verify token signature, expiration, issuer, and audience claims. Never trust client-side validation alone.
Server-side validation is mandatory
Avoid Sensitive Data
Never include passwords, credit card numbers, or other sensitive information in JWT payload. JWTs are encoded, not encrypted.
JWTs are Base64 encoded, easily decoded
Secure Storage
Store JWTs in httpOnly cookies or memory. Avoid localStorage for sensitive tokens due to XSS vulnerability risks.
httpOnly cookies are most secure
Common JWT Use Cases
Discover how JWTs are used across different application scenarios and architectures
User Authentication
The most common JWT use case. After successful login, the server issues a JWT containing user identity and permissions.
Benefits:
- • Stateless authentication
- • No server-side session storage
- • Works across multiple services
- • Mobile-friendly
API Authorization
JWTs carry authorization information allowing APIs to determine what resources a user can access without database lookups.
Features:
- • Role-based access control
- • Permission scoping
- • Reduced database queries
- • Fine-grained access control
Single Sign-On (SSO)
Enable users to access multiple applications with one login. JWTs facilitate secure token sharing across domains and services.
Advantages:
- • Seamless user experience
- • Centralized authentication
- • Cross-domain compatibility
- • Enterprise integration
Secure Information Exchange
JWTs securely transmit information between parties. The signature ensures data integrity and authenticity.
Use Cases:
- • Microservice communication
- • Webhook verification
- • API key alternatives
- • Temporary access tokens