Free Online JWT Debugger & Token Decoder

What is a JSON Web Token (JWT)?

JSON Web Token (JWT) is an open, industry-standard RFC 7519 method for securely representing claims between two parties. It is heavily used in modern web applications for authentication, session management, and information exchange. Because tokens contain encoded JSON payloads, developers constantly need a quick way to inspect what data is stored inside them without manually running command-line scripts or writing custom debugging loops.

Why Use Our Free Online JWT Debugger?

Debugging authentication flows can be frustrating, especially when dealing with opaque authorization headers and expiration timestamps. Our client-side JWT decoder tool offers several distinct advantages:

• 100% Privacy & Security: All decoding happens directly inside your web browser using vanilla JavaScript. Your tokens, secrets, and sensitive user payloads are never transmitted, logged, or stored on any remote server.
• Instant Real-time Feedback: As soon as you paste your encoded string, the tool instantly splits the token into its core components and formats the header and payload with clean syntax indentation.
• Expiration Tracking: The tool automatically inspects the standard exp (expiration) claim and notifies you if the token is currently active or expired.

How to Decode and Inspect a JWT Step-by-Step

Using this utility requires zero installation or configuration. Simply follow these steps:

• Copy your full JSON Web Token from your browser's local storage, API response, or authorization header.
• Paste the token into the input box above.
• Review the automatically formatted JSON objects in the Header and Payload output panels.
• Check the status validation bar at the bottom to verify structural integrity and expiration dates.

Understanding JWT Structure: Header, Payload, and Signature

A standard JWT consists of three distinct parts separated by periods (.):

• The Header: Typically consists of two parts: the type of the token (JWT) and the signing algorithm being used, such as HMAC SHA256 or RSA.
• The Payload: Contains the claims or statements about an entity (typically, the user) and additional metadata like expiration time (exp), issuer (iss), and subject (sub).
• The Signature: Used to verify that the sender of the JWT is who it says it is and to ensure that the message wasn't tampered with along the way.