Paste a JWT (JSON Web Token) and its Header and Payload are decoded into a JSON tree automatically, with exp highlighted and remaining validity days / expiry status calculated. Includes a pure front-end HMAC-SHA256 + Base64URL signature verification, plus a one-click “tamper attempt” that demonstrates how a modified Payload instantly invalidates the signature. Everything runs locally — your token is never uploaded.

（内容由AI生成，仅供参考）