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JWT Debugger

Inspect JWT headers and payloads locally without leaking tokens to third-party tools.

JWT Debugger
Decode JWT headers and payloads locally to inspect claims without sending tokens to a server.
Ctrl+Enter Decode No signature upload Claims summary
Encoded JWT
0 segments | 0 chars
Decoded output Read only JSON
0 lines | 0 keys
Ready Header and payload only
Paste a JWT to inspect its decoded claims locally. Signature verification is not performed on this page.

How ZeroData protects your privacy

  • ✓ No Uploads: Tool input is processed in your browser and is not sent to ZeroData servers.
  • ✓ No Storage: Tool input is not saved by this website.
  • ✓ No Input Tracking: Analytics never receive the text, files, keys, or credentials you process.
  • ✓ Verifiable: Disconnect from the network after the page loads; local tool processing continues without uploading your input.

How to Use the JWT Debugger

  1. Paste a JWT into the token editor.
  2. Use Decode token to inspect the header and payload as JSON.
  3. Review claim summaries such as algorithm, subject, and expiry.
  4. Copy or download the decoded JSON if you need to share the safe, human-readable structure.

Common Use Cases

  • Troubleshooting a '401 Unauthorized' API error by verifying the token's expiration (exp) timestamp.
  • Auditing a JWT generated by an identity provider (like Auth0 or AWS Cognito) to ensure correct user roles are included.
  • Decoding a frontend session token to extract the user's ID or email address without making a backend request.
  • Verifying the signing algorithm (e.g., HS256 vs RS256) specified in the token's header during integration testing.
  • Debugging single sign-on (SSO) integration flows by inspecting the claims passed between microservices.

Frequently Asked Questions

Can someone use this tool to forge or modify a JWT?

No. This tool only decodes the Base64 representation of the token for viewing. To modify a JWT, you would need the server's private secret key to recalculate the cryptographic signature.

Does this tool verify the signature of my token?

No, this tool acts as a decoder to let you inspect the header and payload. It does not require your secret key and therefore does not perform cryptographic signature validation.

Is it safe to paste a live production token here?

Yes. Because the decoding happens entirely in your local browser, the token is never sent to a server, meaning there is zero risk of it being intercepted or logged.

Why does my token payload look like gibberish?

If the payload does not decode into readable JSON, the token might be encrypted (JWE) rather than just encoded (JWS), or it may be malformed and not adhering to the JWT standard.

What is the 'exp' field in the payload?

The 'exp' (expiration) claim is a Unix timestamp indicating exactly when the token will expire and no longer be accepted by the server.

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