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JWT Decoder

Paste a JWT to see its header, payload and expiry. No token is sent anywhere. Signature is NOT verified, use only for inspection.

How JWT Decoder works

JWT decoder splits a JSON Web Token into its three parts, header, payload and signature, and displays the decoded header and payload as formatted JSON, along with the expiry (exp) and issued-at (iat) timestamps in human-readable form. It is the fastest way to inspect what is inside a JWT without writing code.

Important: this tool decodes only. It does not verify the signature against a secret or public key, so it cannot confirm whether the token is authentic or has been tampered with. Paste your JWT here to read its claims, then validate the signature in your backend. The exp claim is compared against your device clock to flag an expired token, but no revocation list is checked.

Frequently asked questions

Is the JWT I paste sent anywhere?

No. Decoding is done entirely in your browser: the tool splits the token on the dot separators, Base64-decodes each part and parses the JSON locally. The token text is never transmitted to Sunasty or any third party.

Does it verify the JWT signature?

No, and this is deliberate. Signature verification requires the secret key (for HMAC algorithms) or the public key (for RSA/ECDSA), which you should never paste into a third-party tool. This decoder reads the payload claims only; validate the signature in your own backend or trusted library.

Why does the expiry timestamp show as "expired"?

The tool compares the exp claim (seconds since Unix epoch) with the current time on your device. If exp is in the past, the token is flagged as expired. This is a local time comparison only, no revocation list is checked.

Does it work offline?

Yes, once the page has loaded. Because the processing happens on your device, you can disconnect from the network and the tool keeps working. This is the clearest proof that your data never leaves your machine.

Is it free? Do I need an account?

It is completely free and requires no sign-up. There are no watermarks, no daily limits and no tracking cookies needed to use the tool.