JWT Decoder Javascript tools
Enter JWT Token
Header
Payload
Signature
Signature verification requires the secret key
Decoded Claims
Token Validation
Verify Signature (Optional)
What is JWT?
JSON Web Token (JWT) is an open standard for securely transmitting information between parties as a JSON object.
JWT Structure
JWTs consist of three parts: Header (algorithm & type), Payload (claims), and Signature (verification).
Common Claims
iss (issuer), sub (subject), aud (audience), exp (expiration), nbf (not before), iat (issued at), jti (JWT ID)
JWT Decoder & Token Analysis Tool
Our JWT Decoder is a comprehensive tool for developers working with JSON Web Tokens. Instantly decode, analyze, and validate JWT tokens used in modern authentication systems. Whether you're debugging API authentication, inspecting token claims, or learning about JWT structure, our tool provides detailed insights into token contents and validity.
What is a JSON Web Token (JWT)?
JSON Web Token (JWT) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. JWTs are widely used for authentication and authorization in web applications, mobile apps, and APIs. They consist of three parts separated by dots: Header.Payload.Signature
JWT Structure Explained
Header (JOSE Header)
Contains metadata about the token type and signing algorithm. Typically includes:
- alg: Signing algorithm (HS256, RS256, ES256, etc.)
- typ: Token type (usually "JWT")
- kid: Key ID for identifying signing key (optional)
Payload (Claims)
Contains the actual data being transmitted. Standard claims include:
- iss: Issuer of the token
- sub: Subject (usually user ID)
- aud: Audience (intended recipient)
- exp: Expiration time
- iat: Issued at time
- nbf: Not valid before time
Signature
Ensures token integrity and authenticity. Created by:
- Encoding header and payload
- Signing with secret key or private key
- Using specified algorithm
Key Features of Our JWT Decoder
- Instant Decoding: Paste any JWT and see decoded contents immediately
- Visual Breakdown: Color-coded display of header, payload, and signature
- Claim Analysis: Detailed view of all token claims with descriptions
- Expiration Check: Automatic validation of token expiration status
- Timestamp Conversion: Human-readable dates for all time-based claims
- Signature Verification: Optional verification with secret key
- Example Tokens: Pre-loaded examples for learning and testing
Common JWT Use Cases
API Authentication
Secure API endpoints by validating JWT tokens in request headers. Stateless authentication for RESTful services.
Single Sign-On (SSO)
Share authentication across multiple applications and domains using JWT tokens as portable credentials.
Session Management
Replace traditional server-side sessions with client-side JWT tokens for scalable applications.
Information Exchange
Securely transmit information between services with signed and optionally encrypted JWT tokens.
JWT Security Best Practices
- Use Strong Secrets: For HMAC algorithms, use cryptographically strong secrets (256+ bits)
- Set Expiration: Always include exp claim to limit token lifetime
- Validate Claims: Check iss, aud, and other claims match expected values
- HTTPS Only: Always transmit JWTs over encrypted connections
- Don't Store Sensitive Data: JWTs are encoded, not encrypted (unless using JWE)
- Implement Refresh Tokens: Use short-lived access tokens with longer refresh tokens
- Blacklist Compromised Tokens: Maintain revocation lists for emergency invalidation
JWT Signing Algorithms
Understanding different signing algorithms helps choose the right one for your use case:
- HS256 (HMAC with SHA-256): Symmetric algorithm using shared secret
- RS256 (RSA with SHA-256): Asymmetric algorithm using public/private key pair
- ES256 (ECDSA with P-256 and SHA-256): Elliptic curve algorithm, smaller signatures
- PS256 (RSA PSS with SHA-256): Probabilistic signature scheme
- none: No signature (avoid in production!)
How to Use the JWT Decoder
- Paste Token: Copy your JWT token and paste it in the input field
- Automatic Decoding: The tool instantly decodes and displays all parts
- Review Header: Check algorithm and token type in the header section
- Analyze Claims: Examine payload claims with automatic formatting
- Check Validity: View expiration status and token age
- Verify Signature: Optionally enter secret key to verify signature
Common JWT Claims Explained
Standard Claims
- iss (Issuer): Who created and signed the token
- sub (Subject): Who the token refers to
- aud (Audience): Who the token is intended for
- exp (Expiration): When the token expires
- nbf (Not Before): Earliest time token is valid
- iat (Issued At): When token was created
- jti (JWT ID): Unique identifier for the token
Common Custom Claims
- name: User's display name
- email: User's email address
- role/roles: User permissions
- scope: OAuth 2.0 scopes
- azp: Authorized party
- nonce: Replay attack prevention
JWT vs Traditional Sessions
Understanding when to use JWTs versus traditional session-based authentication:
- Stateless: JWTs don't require server-side storage
- Scalability: Easy to scale across multiple servers
- Cross-Domain: Work across different domains
- Mobile-Friendly: Ideal for mobile app authentication
- Size Consideration: JWTs can be larger than session IDs
- Revocation: More complex to invalidate than sessions
Frequently Asked Questions
Is it safe to decode JWTs online?
Yes, decoding happens entirely in your browser. No data is sent to our servers. However, never paste production tokens containing sensitive data.
Can I decode encrypted JWTs (JWE)?
This tool handles standard signed JWTs (JWS). Encrypted JWTs require the encryption key and are not supported for security reasons.
Why is my token invalid?
Common reasons include: expired token, malformed structure, incorrect formatting, or corrupted signature.
How do I create a JWT?
JWTs should be created server-side using appropriate libraries for your programming language (jsonwebtoken for Node.js, PyJWT for Python, etc.)