What is a JWT Token?
JWT (JSON Web Token) is a compact, URL-safe token format used for securely transmitting information between parties. It's commonly used for authentication and authorization in web applications and APIs.
🎯 Why Use JWT Tokens?
- Stateless: No need to store session data on server
- Scalable: Works across multiple servers and services
- Self-contained: Contains all necessary information
- Secure: Digitally signed to prevent tampering
- Standardized: RFC 7519 standard ensures compatibility
- Cross-domain: Can be used across different domains
JWT Token Structure
JWT Token Format
Three parts separated by dots: Header.Payload.Signature
📋 Header
Contains metadata about the token and signing algorithm.
"alg": "HS256",
"typ": "JWT"
}
- ✅ Algorithm used for signing
- ✅ Token type (usually "JWT")
- ✅ Additional metadata
📦 Payload
Contains the claims (user data and metadata).
"sub": "1234567890",
"name": "John Doe",
"iat": 1516239022
}
- ✅ User information
- ✅ Expiration time
- ✅ Issued at time
🔐 Signature
Verifies the token hasn't been tampered with.
base64UrlEncode(header) + "." +
base64UrlEncode(payload),
secret
)
- ✅ Prevents tampering
- ✅ Verifies authenticity
- ✅ Ensures integrity
How to Use Our JWT Debugger
🚀 Debug JWT Tokens
Decode, validate, and debug JWT tokens with our free, secure JWT debugger.
🔍 Debug JWT Tokens →Step 1: Enter JWT Token
Paste your JWT token into the input field.
Step 2: Decode Token
Our tool automatically decodes the header and payload.
Step 3: Validate Token
Verify the token signature and check expiration.
Step 4: Review Claims
Examine the payload claims and user information.
JWT Claims Explained
🏷️ Standard Claims
Predefined claims with specific meanings.
- iss (issuer): Who issued the token
- sub (subject): Who the token is about
- aud (audience): Who the token is intended for
- exp (expiration): When the token expires
- nbf (not before): When the token becomes valid
- iat (issued at): When the token was issued
- jti (JWT ID): Unique identifier for the token
👤 User Claims
Custom claims containing user information.
- name: User's full name
- email: User's email address
- role: User's role or permissions
- id: User's unique identifier
- permissions: Array of user permissions
- preferences: User preferences and settings
🔒 Security Claims
Claims related to security and access control.
- scope: OAuth 2.0 scopes
- client_id: OAuth client identifier
- nonce: Random value to prevent replay attacks
- azp: Authorized party
- auth_time: When authentication occurred
- session_id: Session identifier
JWT Security Best Practices
✅ Security Do's
- Use Strong Secrets: Use cryptographically secure random secrets
- Set Short Expiration: Use short expiration times (15-30 minutes)
- Validate on Server: Always validate tokens on the server side
- Use HTTPS: Always transmit tokens over HTTPS
- Store Securely: Store tokens securely (httpOnly cookies)
- Rotate Secrets: Regularly rotate signing secrets
❌ Security Don'ts
- Don't Store Sensitive Data: Avoid storing sensitive information in payload
- Don't Use Weak Secrets: Never use weak or predictable secrets
- Don't Trust Client Validation: Never rely on client-side validation
- Don't Use Long Expiration: Avoid very long expiration times
- Don't Store in localStorage: Avoid storing tokens in localStorage
- Don't Ignore Expiration: Always check token expiration
Common JWT Algorithms
🔐 HMAC Algorithms
Symmetric algorithms using a shared secret.
- HS256: HMAC with SHA-256 (most common)
- HS384: HMAC with SHA-384
- HS512: HMAC with SHA-512
🔑 RSA Algorithms
Asymmetric algorithms using public/private key pairs.
- RS256: RSA with SHA-256
- RS384: RSA with SHA-384
- RS512: RSA with SHA-512
🔒 ECDSA Algorithms
Elliptic curve digital signature algorithms.
- ES256: ECDSA with P-256 and SHA-256
- ES384: ECDSA with P-384 and SHA-384
- ES512: ECDSA with P-521 and SHA-512
Frequently Asked Questions
Is JWT secure?
JWT can be secure when implemented correctly with strong secrets, short expiration times, and proper validation.
How long should JWT tokens last?
JWT tokens should have short expiration times (15-30 minutes) and use refresh tokens for longer sessions.
Can JWT tokens be revoked?
JWT tokens cannot be revoked once issued. Use short expiration times and maintain a blacklist for revoked tokens.
What's the difference between JWT and session tokens?
JWT tokens are self-contained and stateless, while session tokens require server-side storage and are stateful.
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Decode, validate, and debug JWT tokens with our free, secure JWT debugger.
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