Understanding JWT Structures: How to Securely Decode Tokens

Decoding JSON Web Tokens

JSON Web Tokens (JWT) are widely used for stateless authentication and authorization. A JWT consists of three distinct sections separated by dots:

1. Header: Contains metadata about the hashing algorithm and token type.
2. Payload: Houses core user claims, permissions, roles, and expiration details.
3. Signature: Verifies that the sender of the JWT is who it says it is and ensures that the message wasn't changed along the way.

Base64URL Encoding vs. Encryption

A common misconception is that JWTs are encrypted. In reality, header and payload claims are merely encoded using Base64URL. Anyone with access to the token string can read the claims.

• Do not store private secrets (passwords, keys) inside a JWT payload.
• Always verify signatures on your backend server before trusting claim data.

Use our free JWT Decoder to safely inspect claims, headers, and token expiration timestamps without transmitting sensitive auth tokens over network connections.