jwtcheck
Decode JWTs and verify their signatures in the browser
About jwtcheck
jwtcheck is a small web tool for developers who need to inspect JSON Web Tokens. Paste a token and it decodes the header and payload, showing expiry, issuer, claims and common mistakes such as alg:none or a missing exp claim. No signup is required.
The free endpoint only decodes the token and does not check the signature. A paid option at 0.02 USDC on Base actually verifies the signature, supporting HMAC with a shared secret and RSA or ECDSA keys fetched from the issuer's JWKS. The site recommends sending tokens and secrets with POST so they do not end up in a URL.
The product is built by Doormat Capital and submitted to Twelve Tools. Its pitch is a quick, no-friction check of what a token contains, with verification available when you need more than a read-only look.
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