JWTデコーダー

よくある質問

›Does this verify the JWT signature?

No — the decoder shows header and payload only. Signature verification requires the issuer's secret or public key, which we never receive.

›Is my token sent to your servers?

Never. Decoding runs entirely in your browser — tokens stay on your device.

›What algorithms are supported?

Any JWT can be decoded (HS256, RS256, ES256, etc.) — decoding is algorithm-agnostic. Verification is the algorithm-specific step.

›What does each part of a JWT contain?

Header: algorithm and token type. Payload: claims (sub, iat, exp, custom data). Signature: HMAC or signature over header.payload using a secret/key.

›Is the decoder free?

Yes — fully free, no signup.