JWT Decoder

This is a free online tool designed for developers to securely decode and analyze the contents of JSON Web Tokens (JWT). Instantly verify the payload data, algorithm header, and easily check token expirations.

Because tokens usually carry sensitive authentication data, this tool runs entirely on "Client-Side Processing". This ensures that the JWTs you paste are parsed purely by your device's browser and absolutely NO information is transmitted to our servers or saved anywhere online.

1. Paste Token: Take your raw, encoded JWT string (which usually starts with `ey...`) and paste it into the "Encoded JWT" textbox on the left.
2. Instant Parse: The tool will instantly split and decode the token into pretty-printed, syntax-highlighted JSON formats on the right side.
3. Verify Header & Payload: The red "Header" box shows metadata like the algorithm. The purple "Payload" box reveals the actual claims (e.g. user IDs, roles).
4. Expiration Check: If the payload contains standard `exp` or `iat` timestamps, the tool will automatically convert them to your local time. A badge will alert you whether the token is currently "Valid" or "Expired".

JWT (JSON Web Token)

A signed token containing a JSON-formatted payload. Widely used in web applications as a mechanism for authentication and authorization.

Header

The first part of a JWT. Stores the token type (typ) and signing algorithm (alg) information, Base64Url encoded.

Payload

The main data portion of a JWT. Contains claims such as user ID, permissions, expiration (exp), and issued-at (iat) timestamps.

Signature

The tamper-detection portion of a JWT. Created by signing the header and payload with a secret key to guarantee token authenticity.

Base64Url Encoding

An encoding scheme that converts binary data into URL-safe strings. Each part of a JWT (Header, Payload, Signature) is encoded using this scheme.

Claims

Individual items of information within the JWT payload. Includes reserved claims like iss (issuer), sub (subject), exp (expiration), iat (issued-at), and application-specific custom claims.

Expiration (exp)

The UNIX timestamp at which the JWT token becomes invalid. This tool converts this value into a human-readable datetime format for easy verification.

• API Debugging: Verify if your backend authentication server is correctly packing user ID and Roles into the token payload without writing custom decoding scripts.
• Checking 401 Unauthorized Errors: Grab the token from your browser's local storage or developer network tab to instantly check if an expiration timestamp (`exp`) has lapsed.
• Frontend Implementation: Visually confirm the exact JSON structure of the decoded JWT payload to properly map user properties in your frontend React/Vue application.

Q.Is the JWT token I enter sent to a server?

No. JWT decoding is done entirely by JavaScript within the browser. The token is never sent externally, so even sensitive tokens can be safely analyzed.

Q.Can this tool verify the JWT signature?

This tool specializes in decoding (parsing) the structure of a JWT. Signature verification requires a secret key; in production, please perform verification server-side.

Q.Can I decode an already-expired JWT?

Yes. This tool simply decodes and displays the token's contents, so it can parse tokens regardless of expiration status. You can also see at a glance whether the token is expired.

Q.Are the three JWT parts (Header, Payload, Signature) color-coded?

Yes. The Header (red), Payload (purple), and Signature (blue) are visually distinguished, with each part's contents shown as formatted JSON.

Q.What happens if I enter an invalid JWT format?

An error message is displayed and you are guided on what part of the formatting is problematic. Please enter a valid JWT in the "xxx.yyy.zzz" format.

Q.Are UNIX timestamps automatically converted?

Yes. UNIX timestamp values such as exp (expiration) and iat (issued-at) are automatically converted to human-readable datetime format.

Q.Can I use this on a smartphone?

Yes. The tool is responsive, so you can paste, decode, and review JWTs from a smartphone browser as well.