JWT Parser
Professional online JWT token parser, decoder and validator. Decode Header, Payload, and Signature, validate token structure and expiration. 100% secure client-side processing.
JWT Parser
Professional online JWT token parser, decoder and validator. Decode Header, Payload, and Signature, validate token structure and expiration time. 100% client-side processing ensures data security and privacy.
JWT Token Input
Paste your JWT token for parsing and validation
Quick Guide
📋 Header Parsing
View JWT algorithm type, token type and metadata
📄 Payload Parsing
View user info, claims, expiration and other data
✅ Token Validation
Verify token format, time fields and structure
🔒 Security Note
This tool processes 100% locally, no data sent to server
About JWT (JSON Web Token)
JWT (JSON Web Token) is an open standard (RFC 7519) for secure information transmission and authentication. It consists of three parts: Header, Payload, and Signature, separated by dots, making it one of the most widely used token formats in modern web applications.
Main Uses:
- • User authentication
- • API authorization
- • Service-to-service communication
- • Single Sign-On (SSO)
Security Best Practices:
- • Set reasonable expiration time
- • Use secure signing algorithms
- • HTTPS transmission protection
- • Verify signature integrity
JWT Structure Explained:
Header
Contains token type and signing algorithm information like alg and typ fields
Payload
Contains claims information such as user ID, permissions, expiration time
Signature
Used to verify the integrity and authenticity of the token
Common JWT Use Cases
Web Application Authentication
- • User receives JWT token after login
- • Each request includes token for identity verification
- • No need to store session state on server
- • Supports cross-domain and microservices architecture
API Authorization
- • RESTful API access control
- • OAuth 2.0 and OpenID Connect
- • Third-party application integration
- • Fine-grained permission control
Mobile Applications
- • iOS and Android app authentication
- • Offline token verification
- • Reduced server query frequency
- • Enhanced user experience
Microservices Communication
- • Identity propagation between services
- • Distributed system authentication
- • Stateless service design
- • Horizontal scaling support
JWT Signing Algorithm Comparison
Choosing the right signing algorithm is crucial for JWT security. Here's a comparison of common algorithms:
HS256 (HMAC-SHA256)
Type: Symmetric encryption
Security: ⭐⭐⭐⭐
Performance: Excellent
Use case: Monolithic apps, internal services
Requires protecting shared secret key
RS256 (RSA-SHA256)
Type: Asymmetric encryption
Security: ⭐⭐⭐⭐⭐
Performance: Slower
Use case: Distributed systems, public APIs
Public key can be distributed openly
ES256 (ECDSA-SHA256)
Type: Elliptic curve
Security: ⭐⭐⭐⭐⭐
Performance: Fast
Use case: Mobile apps, IoT devices
Shorter key length, better performance
⚠️ Security Warning: Avoid using "none" algorithm as it skips signature verification. Always use strong signing algorithms in production.
JWT Best Practices and Security Guidelines
🔐 Security Best Practices
- ✓Set reasonable expiration times (15min-1hour recommended)
- ✓Always use HTTPS to prevent man-in-the-middle attacks
- ✓Validate all JWT fields on the server side
- ✓Regularly rotate signing keys
- ✓Implement JWT blacklist mechanism
⚠️ Security Warnings
- ✗Never store sensitive information in JWT
- ✗Never use "none" algorithm
- ✗Don't pass JWT in URL parameters
- ✗Don't set overly long expiration times
- ✗Don't skip signature verification
🛡️ Recommended JWT Storage Methods
JWT vs Other Authentication Methods
| Feature | JWT Token | Session Cookie | OAuth Token | API Key |
|---|---|---|---|---|
| Server State | ✅ Stateless | ❌ Stateful | ✅ Stateless | ✅ Stateless |
| Cross-Domain Support | ✅ Native support | ⚠️ Requires config | ✅ Native support | ✅ Native support |
| Mobile Friendly | ✅ Excellent | ⚠️ Limited | ✅ Excellent | ✅ Excellent |
| Security | ⚠️ Medium | ✅ High | ✅ High | ⚠️ Medium |
| Implementation Complexity | ⚠️ Medium | ✅ Simple | ❌ Complex | ✅ Simple |
| Best Use Case | Microservices, APIs | Traditional web apps | Third-party integration | Internal APIs |
Common Errors and Solutions
🔴 "Invalid token format"
Cause: JWT format is incorrect, not a standard three-part structure
Solution: Check if token is complete with header.payload.signature parts
🔴 "Token has expired"
Cause: JWT exp field is less than current time
Solution: Use refresh token to get new JWT, or redirect to login
🔴 "Invalid signature"
Cause: Token was tampered with or wrong key used for verification
Solution: Check signing key is correct and token wasn't modified
🔴 "Algorithm mismatch"
Cause: JWT header alg doesn't match server verification algorithm
Solution: Ensure client and server use the same signing algorithm
Code Examples and Integration Guide
⚡JavaScript Client-side
// JWT decode (for info only, doesn't verify signature)
function parseJWT(token) {
const base64Url = token.split('.')[1];
const base64 = base64Url.replace(/-/g, '+')
.replace(/_/g, '/');
const jsonPayload = decodeURIComponent(
atob(base64).split('').map(function(c) {
return '%' + ('00' + c.charCodeAt(0)
.toString(16)).slice(-2);
}).join('')
);
return JSON.parse(jsonPayload);
}
// Check if token is expired
function isTokenExpired(token) {
const payload = parseJWT(token);
return Date.now() >= payload.exp * 1000;
}🟢Node.js Server-side
const jwt = require('jsonwebtoken');
// Verify JWT token
function verifyToken(token, secret) {
try {
const decoded = jwt.verify(token, secret);
console.log('Token valid:', decoded);
return decoded;
} catch (error) {
if (error.name === 'TokenExpiredError') {
console.log('Token expired');
} else if (error.name === 'JsonWebTokenError') {
console.log('Token invalid');
}
return null;
}
}
// Generate JWT token
function generateToken(payload, secret) {
return jwt.sign(payload, secret, {
expiresIn: '1h',
algorithm: 'HS256'
});
}🔧 Popular JWT Libraries
- • jsonwebtoken
- • jose
- • PyJWT
- • python-jose
- • jjwt
- • java-jwt
- • golang-jwt
- • jose2go
JWT Frequently Asked Questions (FAQ)
Q: Is JWT token secure? Can I store sensitive information in it?
A: JWT Payload is only Base64 encoded, not encrypted, so anyone can decode and view it. Never store passwords, personal sensitive information, or secrets in JWT. JWT security relies primarily on signature verification.
Q: What happens when a JWT token expires?
A: When JWT expires (exp field is less than current time), the server will reject the request. The client needs to use a refresh token to obtain a new JWT or redirect the user to log in again.
Q: How to verify JWT token authenticity?
A: You need to use the same secret key and algorithm used for signing to verify the Signature part. This tool can only parse and format validate - actual signature verification must be done on the server side.
Q: What's the difference between JWT and traditional Sessions?
A: JWT is stateless with all information contained in the token; Sessions require server-side storage. JWT suits distributed and microservices environments while Sessions work better for traditional monolithic applications. JWT supports cross-domain usage while Sessions are typically limited to the same domain.
Q: Is this JWT parser safe to use?
A: Yes, our JWT parser runs 100% locally in your browser and never sends your tokens to any server. All parsing and validation operations are performed on your device, ensuring complete data security and privacy.
Q: Can JWT tokens be revoked?
A: JWT itself is stateless and cannot be directly revoked. However, similar effects can be achieved through maintaining blacklists, shortening expiration times, or using refresh token mechanisms.