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JWTデコーダー

JSON Web Tokenのヘッダーとペイロードをブラウザ内でデコードします。署名は検証しません。

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このツールはブラウザ内で動作します。入力内容、ファイル、生成した値はこの端末に残ります。お気に入りと最近使ったツールを利用する場合も、ローカルストレージに保存されるのはツール名だけで、パスワード、文書、QR コードの内容は保存されません。 詳しくはプライバシーポリシーをご覧ください。

このツールの詳しい解説（使い方、例、よくある質問）は、現在英語のみでご用意しています。

What this tool does

Read the header and payload of one compact JSON Web Token. The signature is not checked.

How to use

  1. Paste a compact token with sections separated by dots.
  2. Press Decode.

Examples

  • A three-part token

    The first part is the header, the second is the payload, and the third is an unchecked signature section.

Main features

  • Decoded header JSON.
  • Decoded payload JSON.
  • A note that says whether a signature section is present.

How it works

The page splits the token on dots and decodes the header and payload from base64url as UTF-8 JSON. A signature section can be reported as present or empty. It is never described as valid or invalid, because this page does not verify it.

Tips

  • Paste the token only in this page.
  • Treat a decoded payload as untrusted until a verifier checks the signature.

Limitations

Decoding does not prove that a token is authentic. The page does not fetch a signing key.

See the disclaimer for what these tools do not cover.

FAQ

What does a JWT decoder show?
It shows the header JSON and the payload JSON. It also says whether a signature section is present.
Does decoding prove the token is authentic?
No. Decoding a JWT does not verify its signature or prove that the token is authentic.
Is the token sent to a server?
No. Decoding happens in your browser. The token is not saved or added to the page address.
What if the signature section is empty?
The page says the section is present and empty. It still does not call the token valid or invalid.
What if a section is not JSON?
The page rejects that token instead of showing a partial guess.

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