JWT Header Decoder

Inspect alg, typ, kid, and other header parameters without uploading the token or treating unverified data as trusted.

JWT

ReadyDecoded Base64URL data is not proof that the token is authentic.

JWT contents are untrusted until signature verification and application-specific claim validation succeed. These browser-local tools do not contact an issuer, fetch keys, or validate authorization policy.

How to use this JWT Header Decoder

Decode and pretty-print the protected header of a compact JWT locally. Enter your values above and the result is calculated directly in your browser. No account is required.

Fast answer, clear inputs

This tool is built around one job: give the answer quickly without forcing a signup or hiding the result. Related tools are linked nearby when the next calculation or conversion is useful.