JWT Generator

A JWT Generator creates signed JSON Web Tokens for use in authentication systems, API security, and information exchange. JWTs allow servers to create tokens that contain verified claims about a user or entity. The token is signed using a cryptographic algorithm, and the signature ensures that the claims have not been altered since the token was issued.

Every JWT begins with a header that specifies the signing algorithm and token type. The generator allows selection from common algorithms including HS256 for HMAC with SHA-256 using a symmetric shared secret, RS256 for RSA with SHA-256 using asymmetric keys, and ES256 for ECDSA with SHA-256. The algorithm choice determines whether a single shared secret or a public-private key pair is required.

The payload section contains the claims that the token is asserting. Standard registered claims are available as preconfigured fields including iss for issuer, sub for subject, aud for audience, exp for expiration time, nbf for not-before time, iat for issued-at time, and jti for unique token identifier. Custom claims can be added for application-specific data such as user roles, permissions, and feature flags.

Developers use the generator to create test tokens during development and testing of authentication systems. Instead of going through the complete login flow each time, a test token with known claims can be created directly for API testing. This accelerates development and makes testing more reproducible.

The expiration time is automatically converted to a Unix timestamp based on the specified duration. Setting appropriate expiration times is a security best practice. Short-lived tokens limit the window of opportunity if a token is compromised. The generator calculates the expiration timestamp from the current time plus the specified duration.

Token signing requires a secret key or key pair depending on the algorithm. For HMAC algorithms, a passphrase or secret string is provided and used to compute the signature. For RSA algorithms, a private key is required to sign the token. The generator accepts keys in PEM format.

The output shows both the encoded JWT string and the decoded components for verification. The generated token can be copied to the clipboard and used immediately in API requests, authentication headers, or application configuration. The decoder preview confirms that the token has been constructed correctly before use.

The generator supports custom header parameters for advanced use cases including kid key identifier for key rotation scenarios, typ for content type specification, and cty for critical extension headers. These advanced options allow the generated tokens to work with complex authentication infrastructures that require additional header metadata.