JWT Decoder & Validator — Decode Header/Payload + Verify HS256/RS256 Signatures Client-Side

Free online JWT decoder and signature validator. Decode header and payload, highlight registered claims (iss/sub/aud/exp/iat/nbf/jti), check expiration in real-time, verify HS256/HS384/HS512 signatures with a shared secret, or RS256/384/512 with a PEM public key. 100% client-side — your tokens never leave the browser. Uses Web Crypto API.