JWT Decoder
What is a JWT Decoder?
A JWT (JSON Web Token) Decoder is a tool that decodes and displays the contents of JWT tokens. JWTs are a compact, URL-safe way to represent claims (information) that are transferred between two parties, commonly used for authentication and authorization in web applications.
JWT tokens consist of three parts separated by dots:
- Header: Contains metadata about the token, such as the algorithm used for signing
- Payload: Contains the claims (user information, permissions, expiration time, etc.)
- Signature: Used to verify the token hasn't been tampered with
JWT decoders are essential for developers debugging authentication issues, understanding what information is stored in tokens, and verifying token structure. However, it's important to note that decoding a JWT only reveals its contents - it doesn't verify the signature. For security, always verify JWTs using the secret key or public key on the server side.
Frequently Asked Questions
Decoding only reveals the token's contents - it doesn't verify the signature. Decoded tokens should never be trusted for authentication without proper signature verification using the secret key.
Common payload fields include user ID, username, email, roles, permissions, and expiration time (exp). The exact fields depend on your application's requirements.
You can decode and view a JWT, but modifying it will invalidate the signature. Modified tokens will be rejected by servers that verify the signature.