JWT Decoder | DevZen

About JWT Decoder

Overview

The JWT Decoder lets you inspect the header, payload claims, and expiration details of any JSON Web Token (JWT) instantly. JWTs are encrypted or encoded tokens used to authenticate users in modern Single Page Applications and APIs. Understanding what data is carried inside a token is key to debugging authentication state.

🔒 Privacy & Security Guarantee

JWTs represent your user authentication signatures. Sending them to a third-party server poses a severe security vulnerability. DevZen decodes JWT signatures entirely within your local browser sandbox. No secrets, keys, or payloads are uploaded or exposed.

Frequently Asked Questions

Why does the tool say my JWT is invalid?+

A valid JWT must consist of three parts separated by periods (Header.Payload.Signature). If any dot is missing, or if the string contains spaces, the decoder will fail to inspect it.

Can this tool verify the signature of my JWT?+

No. Verifying a JWT signature requires the public key or shared secret that signed it. Since this tool operates strictly on the client side for privacy reasons, it parses the token claims but does not validate if the signature has been tampered with.

What is in the Header vs the Payload?+

The Header specifies the metadata (like signature algorithm 'HS256' or 'RS256'). The Payload contains the actual session claims, such as the user ID, name, email, and token expiry time (exp).