JWT Encoder
Build and sign HS256 JSON Web Tokens with a secret.
Signed JWT
How JWT signing works
A JSON Web Token has three Base64URL parts joined by dots: header.payload.signature. This tool builds the header for your chosen HMAC algorithm, encodes your payload, and signs the header.payload string with your secret using the browser's native crypto.subtle HMAC. The secret never leaves your device. Because anyone with the secret can forge tokens, only sign with throwaway secrets here — never paste a production signing key into any web tool.
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