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KioTools
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JWT Decoder & Debugger

What is this tool?

A client-side JWT viewer. It splits the token on its dots, Base64URL-decodes the header and payload, pretty-prints the JSON, and resolves the standard time claims — without ever sending the token anywhere.

When to use it

  • Inspecting what claims an auth token actually carries while debugging
  • Checking a token's expiry when a request is unexpectedly rejected
  • Confirming the algorithm and key id in a token's header
  • Reading the sub, scope or roles claim during API integration work
  • Teaching how JWTs are structured

How to use it

  1. 1Paste the full token (three Base64URL parts separated by dots)
  2. 2Read the decoded header and payload as formatted JSON
  3. 3Check the expiry banner — green if still valid, red if expired
  4. 4Review the issued-at and not-before times if the token has them
  5. 5Never rely on these claims for a security decision without verifying the signature elsewhere

Frequently asked questions

Does this verify the signature?

No. Verifying a signature needs the signing key and is a server-side concern. This tool only decodes, so treat every claim as unverified.

Is my token sent anywhere?

No — decoding happens entirely in your browser tab. The token never leaves your device.

What does 'expired' mean here?

It compares the exp claim (seconds since the epoch) against your device's current time. If exp is in the past, the token is shown as expired.

Which token types work?

Any JWS-format JWT with a JSON header and payload — the common case. Encrypted (JWE) tokens can't be decoded without the key.