JWT Signer & Verifier
Free online JWT signer and verifier. Create tokens with HS256/384/512 or verify signatures locally via Web Crypto — your secret never leaves the browser.
Payload (JSON format)
The secret and content are processed locally in your browser (Web Crypto API) and never uploaded
FAQ
Which signing algorithms are supported?
HS256, HS384 and HS512 (HMAC with SHA-256/384/512), implemented with the browser-native Web Crypto API. Asymmetric algorithms (RS256/ES256) are not supported yet.
Is my secret safe?
Yes. Signing and verification run entirely in your browser via Web Crypto — the secret and payload are never sent to any server.
What are iat and exp?
iat is the issued-at time and exp is the expiration time (Unix seconds). A quick button inserts the current time plus 24 hours, and verification automatically flags expired tokens.
Why does verification say the signature is invalid?
The token does not match the secret: either the key is wrong, or the payload or signature was tampered with. Comparison is done in constant time to resist timing attacks.