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JWT デコーダー

JWT をデコード

ブラウザで動作 · アップロード不要

このツールとページ内の説明は、現在は英語のみです。動作は同じで、すべてブラウザ内で実行されます。

The token never leaves this page.
  • 何も端末から出ません
  • サーバーによるサイズ制限なし
  • 登録不要・透かしなし
  • 無料

How to decode a JWT

  1. Paste the token (with or without "Bearer ").
  2. Read the header, payload and claims; times such as exp and iat are shown as dates.
  3. To check that it is genuine, open "Check the signature" and enter the secret or public key.

Why decode it here?

Tokens are keys to accounts and APIs. Many online decoders send what you paste to a server. This page can't: its security policy blocks every connection, so the token, and any key you enter, stay on your device.

Decoding is not verifying

  • Anyone can read a JWT: the header and payload are only Base64-encoded, not encrypted.
  • Only the signature check proves the token was issued by the key holder and wasn't changed.
  • Supported: HS256/384/512 (shared secret), RS256/384/512, PS256/384/512, ES256/384/512 (public key as PEM or JWK) and EdDSA where the browser supports it.
  • Encrypted tokens (JWE, five parts) can't be read without the private key.

よくある質問

Should I paste a private key?

No, and you never need to: signatures are checked with the public key. Only HMAC tokens (HS256…) use a shared secret.

Is my token uploaded?

No. It is decoded and checked in your browser with the built-in WebCrypto API.