How do I decode a JWT token?

Paste the full JWT token (the long string with two dots separating three parts) into the input field. The tool instantly decodes the header (algorithm, type) and payload (claims, expiration, issuer) without needing any secret key.

Is it safe to paste my JWT token here?

Yes. The decoding happens entirely in your browser using JavaScript — no data is sent to any server. JWTs are encoded (Base64URL), not encrypted, so decoding doesn't require your secret key.

What are the three parts of a JWT?

A JWT has three Base64URL-encoded parts separated by dots: the Header (algorithm and token type), the Payload (claims like user ID, expiration, roles), and the Signature (cryptographic proof the token hasn't been tampered with).

How do I check if my JWT is expired?

Paste your token and look at the exp (expiration) claim in the decoded payload. The tool shows both the raw Unix timestamp and a human-readable date, plus an indicator showing whether the token is currently expired.

JWT デコーダー

JWT のヘッダー・ペイロード・有効期限を表示

JWT Token

Inspect JWT claims without touching production

Authentication bugs are often token bugs — a missing claim, a wrong audience, an expired exp, the wrong algorithm. Decoding a JWT in the browser shows you the header, payload, and expiry instantly without sending the token to any server, so you can debug login, authorization, and API access issues with confidence.

Use the decoder when you need to

Debug an expired or rejected token

Look at the exp, nbf, and iat claims to confirm whether the token is past its lifetime or not yet valid.

Verify the claims your backend expects

Check that the audience, issuer, scopes, and custom claims match what your authorization layer requires.

Audit a token before pasting it into a ticket

Decode the payload to confirm there's nothing sensitive inside before sharing the token in a bug report.

How to decode a JWT quickly

1
Paste the JWT (the long string with two dots) into the input field.
2
Inspect the decoded header, payload, and expiry status.
3
Copy specific claims or the full payload for use in a bug report or test.

Keep going

Decode arbitrary Base64

Use the encoder/decoder when the value isn't a JWT but is still Base64-encoded.

Test an authenticated request

Replay the request that produced the token to verify auth end-to-end.

Format the payload

Beautify the decoded payload before pasting it into another tool.

Validate the payload

Run a syntax check on custom claims if your decoder produced unusual output.

Common JWT debugging workflows

Diagnose 401 errors from an API

Decode the token to see if the expected claim is missing or the audience is wrong.

Check token expiry during integration

Confirm a freshly minted token's expiry matches your auth provider's configured lifetime.

Audit roles and scopes

Verify the user has the right scopes before troubleshooting authorization in your code.

よくある質問

JWT 全体（ドット 2 つで 3 つのパートに区切られた長い文字列）を入力欄に貼り付けます。ツールが即座に header（algorithm, type）と payload（claims, expiration, issuer など）をデコードします。secret key は不要です。

はい。デコード処理は JavaScript によりブラウザ内で完結し、データはサーバーへ送信されません。JWT は暗号化ではなくエンコード（Base64URL）なので、デコードに secret key は必要ありません。

JWT はドットで区切られた 3 つの Base64URL エンコード部分から成ります。Header（アルゴリズムとトークン種別）、Payload（ユーザー ID、期限、ロールなどの claim）、Signature（改ざんされていないことを示す暗号学的な署名）です。

トークンを貼り付け、デコード結果の payload にある exp（expiration）claim を確認します。ツールは Unix タイムスタンプと読みやすい日時の両方を表示し、現在期限切れかどうかの判定も示します。