What is a JSON Web Token (JWT)?

A JSON Web Token (JWT) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. JWTs are digitally signed using a secret (HMAC) or public/private key pair (RSA/ECDSA), which verifies the token's integrity and authenticity.

What are the three parts of a JWT?

A JWT consists of three parts separated by dots: 1) Header - contains the token type and signing algorithm, 2) Payload - contains the claims (user data and metadata), 3) Signature - created by signing the encoded header and payload with a secret key. Each part is Base64Url encoded.

What is the HS256 algorithm?

HS256 (HMAC with SHA-256) is a symmetric signing algorithm where the same secret key is used to both sign and verify the token. It's widely used for JWTs because it's fast, simple, and secure when the secret key is properly protected.

Is this JWT encoder secure?

Yes, our JWT encoder runs entirely in your browser using the jose library. No data is sent to any server - your headers, payloads, and secret keys remain completely private on your device. The signing is performed using secure cryptographic functions.

What claims should I include in my JWT payload?

Common JWT claims include: 'sub' (subject - user identifier), 'iat' (issued at - timestamp), 'exp' (expiration time), 'iss' (issuer), 'aud' (audience), and 'nbf' (not before). You can also add custom claims specific to your application.

How long should my JWT secret key be?

For HS256, your secret key should be at least 32 characters (256 bits) long. Longer keys provide better security. Use a cryptographically random string - avoid dictionary words or predictable patterns. Consider using an API key generator for creating strong secrets.

JWT Encoder | Free Online JSON Web Token Generator & Signer

What is JWT Encoding?

JWT (JSON Web Token) encoding is the process of creating a signed token from a header, payload, and secret key. The header and payload are Base64Url encoded, then combined with a cryptographic signature to produce a compact, URL-safe token that can be used for authentication and secure data exchange between services.

Why Use Our JWT Encoder?

Secure & Private: All encoding happens in your browser - no data sent to servers
Industry Standard: Uses the trusted jose library for JWT operations
Visual Breakdown: See the encoded header, payload, and signature separately
Real-Time Generation: Instant JWT creation with immediate feedback
Developer-Friendly: Copy tokens with one click for easy integration

Understanding JWT Structure

Header: Contains metadata about the token including the signing algorithm (alg) and token type (typ). Example: {"alg": "HS256", "typ": "JWT"}

Payload: Contains the claims - statements about the user and additional metadata. Standard claims include sub (subject), iat (issued at), exp (expiration), and custom claims for your application.

Signature: Created by signing the Base64Url encoded header and payload with your secret key. This ensures the token hasn't been tampered with.

Common JWT Use Cases

Authentication: Store user identity and session data in stateless tokens
Authorization: Include user roles and permissions for access control
API Security: Authenticate API requests without server-side sessions
Single Sign-On (SSO): Share authentication across multiple applications
Information Exchange: Securely transmit data between parties

JWT Best Practices

1. Use strong secrets: Generate cryptographically random secrets with at least 256 bits of entropy for HS256.

2. Set expiration times: Always include an 'exp' claim to limit token validity and reduce security risks.

3. Keep payloads small: JWTs are sent with every request, so minimize payload size for performance.

4. Never store sensitive data: JWTs are encoded, not encrypted. Avoid including passwords or secrets in the payload.

5. Validate tokens properly: Always verify the signature and check expiration on the server side.

Frequently Asked Questions

What is the difference between JWT encoding and encryption?

JWT encoding (signing) ensures data integrity and authenticity - you can verify the token hasn't been modified. Encryption hides the data so it can't be read. Standard JWTs are signed but not encrypted, meaning the payload is readable (just Base64 decoded) but tamper-proof.

Why is my JWT different each time with the same inputs?

If your payload includes dynamic claims like 'iat' (issued at) with the current timestamp, the token will change each time because the payload content is different.

Can I use this JWT in production?

Yes, tokens generated by this tool are valid JWTs. However, ensure you use a strong, unique secret key in production and never expose it publicly.

What algorithms are supported?

This encoder supports HS256 (HMAC with SHA-256), which is the most widely used symmetric signing algorithm for JWTs. For asymmetric algorithms like RS256, you would need public/private key pairs.