Build and HMAC-sign a JSON Web Token in the browser.
The reverse of the JWT Decoder: build a JSON Web Token from a header and a payload, sign it with HMAC, and get the signed token back. Everything runs in your browser with WebCrypto — the secret never leaves the page.
Never sign a real token with a production secret in a browser tool — for anything real, sign on your server. none means no signature at all and is rejected by every real verifier.