JWT Sign (HS256 / RS256)
Sign a JSON Web Token with HS256 (HMAC shared secret) or RS256 (RSA private key). Output is a standard compact JWT (header.payload.signature).
Private: Your HMAC secret or RSA private key never leaves this device. Pure client-side signing.
Signing runs entirely in your browser. The HMAC secret or RSA private key never leaves this device.
HS256 (HMAC + shared secret)
RS256 (RSA private key PEM)
A JSON Web Token (JWT) is three base64url segments: header.payload.signature. The header says which algorithm to use; the payload is your claims; the signature is the HMAC or RSA signature over the first two segments.
This tool builds the header and payload in the browser, then signs with Web Crypto (HMAC for HS256, RSASSA for RS256). Nothing is sent to a server.