WebToolArcJWT Header Decoder
Inspect alg, typ, kid, and other header parameters without uploading the token or treating unverified data as trusted.
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.
JWT header policy & signing metadata audit
Use the token already pasted in the decoder above, then inspect the signing metadata as a security handoff: algorithm, type, key identifier and signature-segment size. Compare the header with an expected algorithm instead of treating readable Base64URL as proof of authenticity.
| Header field | Value | Policy check | Why it matters |
|---|
Decoding is not signature verification. A readable JWT can still be forged or use an unexpected algorithm; verify signatures with the issuer key in the application that trusts the token.