Question 1

What is a JWT token?

Accepted Answer

A JSON Web Token (JWT) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. JWTs are commonly used for authentication and authorization in web applications. They consist of three parts: a header, payload, and signature, separated by dots.

Question 2

How do I decode a JWT token?

Accepted Answer

To decode a JWT token, paste your token into the input field and click 'Decode JWT'. The tool will instantly show you the header (containing algorithm and token type), the payload (containing claims like user data, expiration time), and the signature. No secret key is required for decoding.

Question 3

Is it safe to decode JWT tokens online?

Accepted Answer

This JWT decoder is 100% client-side, meaning your tokens are never sent to any server. All decoding happens directly in your browser using JavaScript. This makes it completely safe to decode even sensitive tokens, as they never leave your device.

Question 4

What are JWT claims?

Accepted Answer

JWT claims are pieces of information asserted about a subject. Common claims include 'iss' (issuer), 'sub' (subject), 'aud' (audience), 'exp' (expiration time), 'iat' (issued at), and 'nbf' (not before). Custom claims can also be added to store application-specific data.

Question 5

Why can't I verify JWT signatures with this tool?

Accepted Answer

JWT signature verification requires the secret key (for HMAC algorithms) or public key (for RSA/ECDSA algorithms). For security reasons, this client-side tool does not perform signature verification, as exposing secret keys in a browser would be insecure. Use server-side verification in your applications.