JWT Token Decoder & Analyzer
Decode and analyze JSON Web Tokens (JWTs) to understand their structure, claims, and expiration. Educational tool for JWT debugging and analysis.
Interactive Tool
Security Notice
- • This tool only decodes JWT tokens, it does not verify signatures
- • Never share sensitive JWT tokens with untrusted parties
- • JWT tokens may contain sensitive information in the payload
- • This tool is for educational and debugging purposes only
- • Always use HTTPS when transmitting JWT tokens
About JWT Tokens
JSON Web Tokens (JWTs) are compact, URL-safe means of representing claims to be transferred between two parties. They consist of three parts: header (algorithm and token type), payload (claims), and signature (for verification). JWTs are commonly used for authentication and authorization in web applications and APIs.
How to Use
How to Use the JWT Decoder
- Paste JWT Token: Copy and paste your JWT token into the input field
- Click Decode: Click the "Decode JWT" button to analyze the token
- Review Results: Examine the decoded header, payload, and signature
- Check Status: Verify the token's validity and expiration status
- Copy Information: Use the copy buttons to copy specific sections
- Analyze Claims: Review standard claims and custom data
Understanding the Results
Token Status
- Valid: Token format is correct and not expired
- Expired: Token has passed its expiration time
- Invalid: Token format is incorrect or corrupted
Header Information
- Algorithm: Signing algorithm used (HS256, RS256, etc.)
- Token Type: Usually "JWT"
- Key ID: Identifier for the signing key (if present)
Payload Claims
- Standard Claims: iss, sub, aud, exp, iat, nbf
- Custom Claims: Application-specific data
- User Information: User roles, permissions, etc.
Common Use Cases
Common Use Cases
Debugging Authentication
Troubleshoot authentication issues by examining JWT token contents and expiration.
API Development
Verify JWT tokens during API development and testing phases.
Security Analysis
Analyze JWT tokens for security vulnerabilities and improper configurations.
Educational Purposes
Learn about JWT structure and claims for educational and training purposes.
Penetration Testing
Examine JWT tokens during authorized security assessments and penetration testing.
Token Validation
Validate JWT token format and check for proper claim structure.
About This Tool
What are JWT Tokens?
JSON Web Tokens (JWTs) are compact, URL-safe means of representing claims to be transferred between two parties. They are commonly used for authentication and authorization in web applications and APIs.
JWT Structure
Every JWT consists of three parts separated by dots (.)
Header
Contains metadata about the token, including the signing algorithm and token type.
- • Algorithm (alg)
- • Token type (typ)
- • Key ID (kid)
Payload
Contains the claims (data) about the subject. Can include standard and custom claims.
- • Standard claims (iss, sub, aud, exp, iat, nbf)
- • Custom claims
- • User information
Signature
Used to verify the token hasn't been tampered with. Created using the header, payload, and secret key.
- • HMAC with SHA-256
- • RSA signatures
- • ECDSA signatures
Standard JWT Claims
| Claim | Description | Example |
|---|---|---|
| iss | Issuer - who created the token | "auth0.com" |
| sub | Subject - who the token is about | "user123" |
| aud | Audience - intended recipient | "api.example.com" |
| exp | Expiration time - when token becomes invalid | 1640995200 |
| iat | Issued at - when token was created | 1640908800 |
| nbf | Not before - when token becomes valid | 1640908800 |
Technical Details
Technical Implementation
This JWT decoder uses client-side JavaScript to decode JWT tokens without sending them to external servers, ensuring privacy and security.
Decoding Process
- Token Parsing: Split the JWT into header, payload, and signature parts
- Base64 URL Decoding: Convert Base64URL-encoded parts to readable JSON
- JSON Parsing: Parse the decoded header and payload as JSON objects
- Claim Analysis: Extract and analyze standard and custom claims
- Expiration Check: Compare expiration time with current time
Supported Features
| Feature | Description | Status |
|---|---|---|
| Header Decoding | Decode and display JWT header information | ✓ Supported |
| Payload Decoding | Decode and display JWT payload claims | ✓ Supported |
| Signature Display | Display the JWT signature (Base64 encoded) | ✓ Supported |
| Expiration Check | Check if token is expired based on exp claim | ✓ Supported |
| Signature Verification | Verify token signature with secret key | ✗ Not Supported |
Base64 URL Decoding
The tool implements Base64URL decoding which:
- Replaces hyphens (-) with plus signs (+)
- Replaces underscores (_) with forward slashes (/)
- Adds padding (=) if necessary
- Handles UTF-8 encoding for international characters
Error Handling
- Invalid Format: Detects malformed JWT tokens
- JSON Parsing: Handles invalid JSON in header or payload
- Encoding Issues: Manages Base64URL decoding errors
- Missing Claims: Gracefully handles missing standard claims
Security Considerations
Security Considerations
🚫 Important Limitations
- • This tool only decodes JWT tokens, it does NOT verify signatures
- • Decoded tokens may contain sensitive information
- • Never share production JWT tokens with untrusted parties
- • This tool is for educational and debugging purposes only
⚠️ Privacy & Security
- • All processing is done locally in your browser
- • No JWT tokens are sent to external servers
- • Results are temporary and not stored
- • Be cautious with tokens containing sensitive data
✅ Best Practices
- • Use HTTPS for all JWT token transmission
- • Implement proper token expiration times
- • Use strong signing algorithms (RS256, ES256)
- • Keep signing keys secure and rotate regularly
- • Validate tokens on the server side
- • Use short-lived tokens for sensitive operations
🔒 JWT Security Tips
- • Avoid storing sensitive data in JWT payloads
- • Use appropriate token expiration times
- • Implement token refresh mechanisms
- • Validate all claims on the server side
- • Use secure random secrets for signing
- • Consider using asymmetric algorithms for better security
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