A JSON Web Token (JWT) is a compact, URL-safe token format used for securely transmitting information between parties. It consists of three Base64-encoded parts: a header (algorithm and type), a payload (claims/data), and a signature.

Yes, with our tool it is completely safe. All decoding happens in your browser using JavaScript — no data is sent to any server. However, never share JWT tokens that contain sensitive information in tools that do not guarantee client-side processing.

This tool decodes and inspects the JWT structure, but does not verify signatures. Signature verification requires the secret key or public key, which should never be entered into a web-based tool for security reasons.

Common registered claims include: iss (issuer), sub (subject), aud (audience), exp (expiration time), nbf (not before), iat (issued at), and jti (JWT ID). Custom claims can also be added to the payload.

When a JWT token expires (the current time exceeds the "exp" claim), it should no longer be accepted by the server. This is a security mechanism to limit the window of token misuse. Expired tokens need to be refreshed or a new login is required.