Decode a JSON Web Token to read its header and payload without any server round trip. A JWT is three Base64url segments separated by dots: a header describing the algorithm, a payload of claims and a signature. This decoder splits the token, Base64url-decodes the first two parts and pretty-prints them as JSON so you can inspect the issuer, subject, scopes and expiry while debugging auth. It also translates the exp and iat timestamps into readable dates so you can see at a glance whether a token is expired. Note that this tool does not verify the signature, since that requires the secret or public key; it is a decoder for inspection. Everything runs locally, so your tokens never leave the browser.