A JSON Web Token (JWT) is a compact string used to securely pass information between systems, commonly for login sessions and API authentication. A JWT has three parts separated by dots: a header (which describes the algorithm), a payload (which contains claims like user ID or expiry time), and a signature (which proves the token hasn’t been altered). Each part is encoded using Base64URL (a URL-safe version of Base64 that replaces + with - and / with _).
⚠️ Security notice: Be careful where you paste or share JWTs — they can contain sensitive information and act as keys to systems or data. This tool processes everything locally in your browser — no data is stored, logged, or sent to any server.