JWT Decoder
Decode JWT tokens and verify HS256 & RS256 signatures. Check token expiration and claims.
For HS256 signature verification
PEM format for RS256 verification
Decoded results will appear here
About JWT Decoder
A JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. JWTs are commonly used for authentication and information exchange in modern web applications. Our JWT Decoder tool allows you to decode, verify, and inspect JWT tokens instantly without any installation or setup.
What is a JSON Web Token (JWT)?
JSON Web Tokens are an open industry standard (RFC 7519) method for representing claims securely between two parties. A JWT consists of three parts separated by dots: Header, Payload, and Signature. The header typically contains the token type (JWT) and the signing algorithm (e.g., HMAC SHA256 or RSA). The payload contains the claims or statements about an entity (typically the user) and additional data. The signature is used to verify that the sender of the JWT is who it says it is and to ensure that the message wasn't changed along the way.
How to Use This JWT Decoder
- Paste your JWT token into the input field above
- The tool automatically decodes and displays the header and payload
- View the decoded JSON data in a readable format
- Check token expiration and validity dates
- Copy individual sections for further analysis
- No data is sent to any server - everything happens in your browser
Common JWT Use Cases
- Authentication: After user login, each subsequent request includes the JWT, allowing access to routes and resources
- Information Exchange: JWTs are a secure way to transmit information between parties
- Single Sign-On (SSO): JWTs enable users to sign in once and access multiple applications
- API Authorization: Protect API endpoints by validating JWT tokens
- Mobile Applications: Stateless authentication for mobile apps
- Microservices: Secure communication between distributed services
JWT Structure Explained
A JWT contains three Base64-encoded parts: HEADER.PAYLOAD.SIGNATURE. The header describes the cryptographic operations applied to the JWT. The payload contains claims about the entity and additional data. Standard claims include iss (issuer), exp (expiration time), sub (subject), and aud (audience). The signature ensures the token hasn't been altered and verifies the sender's identity.
Security Best Practices
- Always validate the signature before trusting the token
- Use HTTPS to prevent token interception
- Set appropriate expiration times (exp claim)
- Never store sensitive data in the payload - it's only Base64 encoded
- Use strong signing algorithms (RS256 recommended over HS256)
- Implement token refresh mechanisms for long-lived sessions
- Validate all claims (iss, aud, exp) on the server side
- Store tokens securely (HttpOnly cookies or secure storage)
Common JWT Claims
- iss (issuer): Identifies who issued the token
- sub (subject): Identifies the subject of the token (usually user ID)
- aud (audience): Identifies the recipients that the JWT is intended for
- exp (expiration time): Time after which the JWT expires
- nbf (not before): Time before which the JWT must not be accepted
- iat (issued at): Time at which the JWT was issued
- jti (JWT ID): Unique identifier for the JWT
Frequently Asked Questions
Is it safe to decode my JWT token here?
Yes, absolutely! This tool runs entirely in your browser using client-side JavaScript. No data is transmitted to any server. Your JWT tokens never leave your computer, ensuring complete privacy and security.
What's the difference between JWT and session-based authentication?
JWTs are stateless - the server doesn't need to store session information. All necessary data is contained in the token itself. Session-based authentication requires server-side storage of session data. JWTs are ideal for distributed systems, APIs, and mobile apps, while sessions work better for traditional web applications with server-side rendering.
Can I verify the JWT signature with this tool?
This tool decodes and displays the JWT contents. For signature verification, you need the secret key or public key (for asymmetric algorithms), which should never be shared or entered into online tools. Signature verification should be done server-side in your application.
Why does my JWT look like random characters?
JWTs use Base64 URL encoding to convert JSON objects into a URL-safe string format. When you decode it with this tool, you'll see the original JSON data. The encoding ensures JWTs can be safely transmitted in URLs, HTTP headers, and other contexts where special characters might cause issues.
What should I do if my JWT token is expired?
An expired token (exp claim is in the past) should not be accepted by your application. You need to obtain a new token, either by re-authenticating or using a refresh token if your system implements token refresh functionality. Never extend the expiration time of an existing token client-side.
What are the main JWT signing algorithms?
The most common algorithms are HS256 (HMAC with SHA-256, symmetric), RS256 (RSA Signature with SHA-256, asymmetric), and ES256 (ECDSA with SHA-256, asymmetric). RS256 is recommended for most applications as it uses public/private key pairs, making it more secure for distributed systems where multiple services need to verify tokens.
Can I use this tool for production debugging?
Yes! This tool is perfect for debugging JWT issues in development and production. You can quickly inspect token contents, check expiration times, and verify the structure. However, remember never to share your JWTs publicly or paste them into untrusted tools, as they may contain sensitive information.
How long should a JWT token be valid?
Access tokens should be short-lived (5-15 minutes) to minimize security risks if compromised. Refresh tokens can be longer-lived (days or weeks) but should be stored securely and rotated regularly. The exact duration depends on your security requirements and user experience considerations.