JWT Debugger

What is a JWT?

A JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted.

Structure of a JWT

In its compact form, JSON Web Tokens consist of three parts separated by dots (.):

• Header: Typically consists of two parts: the type of the token, which is JWT, and the signing algorithm being used, such as HMAC SHA256 or RSA.
• Payload: Contains the claims. Claims are statements about an entity (typically, the user) and additional data. There are three types of claims: registered, public, and private claims.
• Signature: To create the signature part you have to take the encoded header, the encoded payload, a secret, the algorithm specified in the header, and sign that.

When should I use JWTs?

JWTs are commonly used for Authorization and Information Exchange. For instance, once a user is logged in, each subsequent request will include the JWT, allowing the user to access routes, services, and resources that are permitted with that token. Single Sign On is a feature that widely uses JWT nowadays, because of its small overhead and its ability to be easily used across different domains.

Security Note

While anyone can decode a JWT, only those with the secret key can verify the signature. You should never put sensitive information (like passwords) in the payload unless it is encrypted. This debugger runs entirely in your browser; your tokens never leave your machine.