Decode a standard header
token = eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.xxx
Result: {"alg":"HS256","typ":"JWT"}
JWT Header Decoder
Extract and decode the JWT header to see the algorithm (alg), token type (typ), and any additional header parameters like kid (key ID). Runs entirely in your browser.
Privacy: this tool processes your data entirely in your browser. Nothing you paste or type is sent to the server.
Enter your values and press Calculate — the result appears here.
Worked examples
Frequently asked questions
What does "alg" mean in the header?
The "alg" (algorithm) field tells you which algorithm was used to sign the JWT. Common values include HS256 (HMAC-SHA256), RS256 (RSA-SHA256), and ES256 (ECDSA P-256).
What is "kid"?
"kid" (Key ID) is an optional header parameter that identifies which key was used to sign the token. It helps issuers rotate keys without breaking existing tokens.
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