JWT Token Decoder
Instantly decode, inspect, and verify JWT tokens online for secure API debugging, authentication testing, and token analysis—client-side processing for privacy.
Our JWT Token Decoder is a free, browser-based tool designed for developers and security professionals to decode JSON Web Tokens (JWTs) in real-time. Whether troubleshooting API authentication, auditing payloads for sensitive claims, or verifying signatures against tampering, this tool provides instant insights into header, payload, and signature components without compromising token privacy.
Common Use Cases for JWT Decoding
- ✓API Authentication Debugging
Quickly decode JWTs to troubleshoot authentication flows in Node.js or React apps during development.
- ✓Security Audits
Inspect token payloads and verify signatures to identify vulnerabilities in API endpoints.
- ✓Token Validation Testing
Simulate expired or tampered JWTs to ensure robust verification in microservices architectures.
- ✓Frontend Integration
Decode user claims from JWTs in browser-based apps for role-based access control without backend calls.
- ✓DevOps Workflows
Analyze tokens in CI/CD pipelines to validate secure handoffs between services like Kubernetes and OAuth.
- ✓Compliance Checks
Review encoded data for privacy compliance in GDPR or CCPA scenarios during app reviews.
Why Choose Our JWT Decoder?
Real-Time JWT Decoding
Paste any JWT token for instant breakdown of header, payload, and signature without delays or submissions
Signature Verification
Validate HMAC, RSA, or ECDSA signatures using your secret key or public certificate for full integrity checks
Detailed Token Inspection
View Base64-decoded JSON structures, expiration times, issuer claims, and custom fields with syntax highlighting
Multi-Language Code Snippets
Generate ready-to-use decoding code for JavaScript, Python, Java, PHP, and more to integrate into your stack
Privacy-Focused Client-Side
All processing happens in-browser—no server uploads—ensuring sensitive tokens stay secure on your device
Error Highlighting
Spot invalid structures, mismatched signatures, or expired tokens with clear alerts and explanations
How to Use the JWT Token Decoder
- Paste Your Token: Enter a JWT string (e.g., eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...) into the input field
- Decode Instantly: The tool automatically parses and displays header, payload, and raw signature sections
- Verify Signature (Optional): Input your secret key or public key and select the algorithm for validation
- Inspect Details: Review claims like iss (issuer), exp (expiration), sub (subject), and custom data with JSON formatting
- Export Insights: Copy decoded JSON or generate code snippets for your preferred language
Understanding JWT Structure
A JWT consists of three Base64-encoded parts separated by dots: Header (algorithm and type), Payload (claims data), and Signature (integrity hash). This compact format enables stateless authentication in distributed systems like SPAs and microservices.
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM1NTkifQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c- Header: {"alg":"HS256","typ":"JWT"} – Specifies signing method
- Payload: {"sub":"1234567890","name":"John Doe","iat":1516239022} – User claims and metadata
- Signature: HMAC-SHA256 of header.payload with secret – Verifies authenticity
This tool decodes without execution risks, helping validate against common pitfalls like weak alg (none) or exposed secrets in regex patterns like /^[A-Za-z0-9-_]+\.[A-Za-z0-9-_]+\.[A-Za-z0-9-_]+$/.
Advanced Features & Capabilities
Live Validation
As you type or adjust keys, the tool re-verifies signatures and highlights issues like invalid alg or expired exp claims in real-time.
Claim Analysis
Automatically detects standard claims (aud, nbf, jti) and flags potential security risks such as nested JWTs or oversized payloads.
Export Options
Download decoded payloads as JSON/CSV or copy full token structures for logging in tools like Postman or Insomnia.
Frequently Asked Questions
What is a JSON Web Token (JWT)?
A JWT is a secure token format used to transmit claims between parties as a JSON object. It is commonly used in modern web applications for authentication and authorization, consisting of header, payload, and signature parts.
Can I decode a JWT without a secret key?
Yes! You can decode the header and payload of a JWT without a secret key. However, verifying the signature for complete security requires the correct secret or public key to ensure the token hasn't been tampered with.
Is my data safe when using JWT tokens?
JWT tokens maintain data integrity through signature verification. Always use strong secret keys, implement token expiration, and follow security best practices like HTTPS transmission for optimal protection against interception or forgery.
What algorithms does the decoder support?
The tool supports common JWT algorithms including HS256 (HMAC-SHA256), RS256 (RSA-SHA256), ES256 (ECDSA-SHA256), and more. Select your algorithm during verification for accurate signature checks.
How do I handle expired JWTs?
The decoder highlights expiration (exp claim) in the payload. For production, always implement server-side checks to reject expired tokens, preventing unauthorized access post-logout.
Can this tool generate JWTs too?
This focuses on decoding and verification; for generation, explore related tools like our API key generators. For custom signing, use libraries like jsonwebtoken in Node.js with secure practices.
Security & Privacy Considerations
This JWT decoder processes everything client-side to protect sensitive tokens from exposure:
- Client-Side Only: No tokens are sent to servers, aligning with zero-trust principles and avoiding data leaks
- Secure Verification: Uses Web Crypto API for signature checks, supporting secure key handling without storage
- Best Practices: Never paste production secrets here; use for dev/testing. Rotate keys regularly and enforce short token lifespans
- Broader Security: Combine with tools like Password Strength Checker or Hash Generator for comprehensive API safeguards
Integration & API Usage
Embed JWT decoding in your JavaScript apps with libraries like jsonwebtoken for server-side or jose for client-side processing:
JavaScript Example (Node.js with jsonwebtoken):
const jwt = require('jsonwebtoken');
// Sample JWT token
const token = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c';
// Secret key for verification
const secret = 'your-secret-key';
// Decode without verification (header + payload)
const decoded = jwt.decode(token);
console.log('Decoded:', decoded);
// Verify signature
try {
const verified = jwt.verify(token, secret);
console.log('Verified Payload:', verified);
} catch (err) {
console.error('Verification failed:', err.message);
}