JWT Decoder

JWTの解読と検査。署名は検証しません。
This tool only decodes JWTs — it does NOT verify signatures. Never paste production tokens with sensitive data.

Decode & Inspect

View header, payload, and signature.

Expiration Check

Shows if token is expired with timestamps.

No Verification

Decodes only — never sends token to server.

Client-side

All processing in your browser. No data uploaded.

JWT Decoderについて

JSON Web Tokens (JWTs) are a compact, URL-safe standard for transmitting signed claims between parties, defined in RFC 7519. A JWT consists of three Base64URL-encoded parts separated by dots: the header (algorithm and token type), the payload (claims such as user ID, roles, and expiration time), and the signature. They are widely used in authentication flows — an API server issues a JWT after login, and the client includes it in every subsequent request so the server can verify identity without querying a database. This decoder lets you instantly inspect any JWT's contents. Paste a token and the tool decodes and pretty-prints the header and payload as formatted JSON, so you can read all the claims at a glance. Timestamp claims (exp, iat, nbf) are automatically rendered as human-readable dates, and expired tokens are flagged in red. Importantly, this tool never sends your token to any server — everything is decoded locally in your browser. Signature verification is intentionally not performed, keeping the tool simple and safe for inspecting tokens without needing a secret key.

JWT Decoderの使い方

  1. Paste your JWT (starting with "eyJ...") into the text area at the top of the tool.
  2. The header and payload are decoded and displayed as formatted JSON automatically.
  3. Check the coloured badges near the top for expiration (exp), issued-at (iat), and not-before (nbf) times.
  4. A red "Expired" badge indicates the token's exp claim is in the past.
  5. Use the Copy buttons to copy the header or payload JSON to your clipboard.
  6. Inspect claim fields such as sub (subject/user ID), iss (issuer), and aud (audience) in the payload section.

よくある質問

Does this tool verify JWT signatures?

No. This tool only decodes the Base64URL-encoded parts of the token — it does not verify the cryptographic signature. Signature verification requires the server's secret key or public certificate and should be done server-side.

Is it safe to paste my JWT here?

Be cautious with production tokens containing sensitive user data. This tool processes everything locally in your browser and never sends data to any server, but avoid pasting tokens from live production systems if possible. Use test or development tokens for inspection.

What are the standard JWT claims?

Common registered claims include: iss (issuer), sub (subject), aud (audience), exp (expiration time), nbf (not before), iat (issued at), and jti (JWT ID). Payloads often also include custom application-specific claims.

What does "exp" mean and why is it important?

The exp claim specifies the expiration time of the token as a Unix timestamp. After this time the token should no longer be accepted. This tool highlights expired tokens in red so you can immediately see if a token has lapsed.

What algorithms can JWTs use?

The algorithm is specified in the header's "alg" field. Common options are HS256 (HMAC-SHA256, symmetric), RS256 (RSA-SHA256, asymmetric), and ES256 (ECDSA-SHA256). The "none" algorithm is considered insecure and should be rejected by servers.

JWT Decoderの完全ガイド：無料オンラインツール

ブラウザ完結で安全・高速なJWT Decoder。開発者やクリエイターの作業を効率化

JWTの解読と検査。署名は検証しません。を瞬時に実現する無料ツールです。面倒なソフトのインストールは不要で、安全にブラウザ上で処理できます。

JWT Decoderが選ばれる理由

  • 高速処理: ミリ秒単位で即時実行。
  • プライバシー保護: データは端末外に送信されません。
  • 完全無料: 登録不要で制限なく利用可能。

簡単な3つの利用手順

  1. JWT Decoderのページを開きます。
  2. データを入力または貼り付けます。
  3. 結果を確認してコピーまたは保存します。

機能比較

項目 Metoolzy JWT Decoder 他社オンラインツール 専用ソフト
料金 完全無料 制限あり 有料ライセンス
セキュリティ 完全ローカル処理 サーバー送信あり ローカル処理

主な活用シーン

  • エンジニアの開発・デバッグ効率化
  • Web制作者の日常作業
  • データ変換・最適化

よくある質問 (FAQ)

入力したデータは保存されますか？

いいえ、すべてブラウザ内で処理され保存されません。