Lumarc DevTools

Security Tools

JWT Decoder

Decode JWT header and payload JSON locally without claiming signature verification.

Processed locally — your data never leaves this browser. Input: JWT token Output: Decoded header and payload
JWT token

Processed locally — your data never leaves this browser.

Decoded header and payload

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Example input and output

Unsigned example token

eyJhbGciOiJub25lIn0.eyJzdWIiOiIxMjMifQ.
Header:
{
  "alg": "none"
}

Payload:
{
  "sub": "123"
}

How to use JWT Decoder

Paste or enter your jwt token, adjust any options, then run the tool. The result appears in the output panel where you can copy or download it.

Related guides

What this tool does

The JWT Decoder splits a JSON Web Token into header and payload sections, decodes Base64URL data and formats the JSON for inspection. It is free to use and designed for technical workflows where pasted data should stay private.

Common use cases

  • Inspect token claims during debugging
  • Read token expiry fields
  • Teach JWT structure safely

Privacy and security

Processed locally — your data never leaves this browser. Lumarc DevTools does not include a backend, account system or hidden analytics in this initial release.

Limitations

  • Signature verification and key fetching are intentionally not included.

Frequently asked questions

Does this verify JWT signatures?

No. Decoding a JWT only shows its contents; it does not prove the token is authentic.