Decode, verify, sign, and assess JSON Web Tokens locally in your browser.
This client-side JWT verifier decodes token contents, validates signatures when you provide the expected key, and highlights implementation risks commonly tested during JWT security reviews.
Signature and algorithm issues, including unsigned tokens, algorithm confusion indicators, weak HMAC secrets, and suspicious ECDSA signatures.
Claim quality issues, including missing or expired expiry, future not-before values, long-lived tokens, missing issuer, missing audience, and privileged claims.
Header trust issues, including attacker-controlled key references such as `kid`, `jku`, `x5u`, and embedded `jwk` values.
Information exposure patterns, including secrets, passwords, API keys, tokens, and personally identifiable data in the readable payload.
The token and key material stay in your browser. Do not paste production secrets into third-party tools unless you understand and accept the risk.
No. Decoding only reads the Base64URL-encoded header and payload. Verification checks that the signature matches the expected key and algorithm, and that claims such as issuer, audience, and expiry are acceptable.
This tool runs locally in your browser, but JWTs can contain sensitive information. Avoid pasting production access tokens or secrets into any tool unless you understand the risk and have permission to analyze them.
The verifier highlights common JWT risks such as unsigned tokens, algorithm confusion indicators, weak HMAC secrets, suspicious key headers, missing expiry, long-lived tokens, and sensitive data in the payload.
No. JWT payloads are readable by clients and anyone who receives the token. Keep passwords, API keys, private keys, refresh tokens, and sensitive personal data out of JWT payloads.
Applications should enforce an explicit server-side allowlist of expected algorithms and key types. Do not trust the token header alone, and reject unsigned tokens in production.