HTTPステータスコード
その番号の意味と、いつ返すか。
- コード数
- 38
出力
1xx informational — the request was received and work continues
2xx success — it worked
3xx redirection — look somewhere else
4xx the request is wrong — the client can usually fix it
5xx the server is wrong — the client can only retry
100 Continue
Carry on sending the body; the headers were acceptable.
101 Switching Protocols
Agreed — usually the handshake into a WebSocket.
200 OK
It worked, and the body is the answer.
201 Created
It worked and something new exists; Location says where.
202 Accepted
Taken in, not done yet. Nothing promises it will succeed.
204 No Content
It worked and there is deliberately nothing to send back.
206 Partial Content
Here is the range you asked for — how video seeking works.
301 Moved Permanently
Use the new address from now on; search engines move their index.
302 Found
Temporarily elsewhere. Keep using this address.
303 See Other
Done — now GET that other address. The answer to a form POST.
304 Not Modified
Your copy is current; nothing is sent. The point of caching.
307 Temporary Redirect
Like 302 but the method must not change.
308 Permanent Redirect
Like 301 but the method must not change.
400 Bad Request
The request itself is malformed. Not the same as invalid data.
401 Unauthorized
Not authenticated. Misnamed: it means “who are you?”.
402 Payment Required
Reserved for years, now used by some APIs for quota and billing.
403 Forbidden
Authenticated and still not allowed. “I know who you are; no.”
404 Not Found
Nothing here, and nothing said about whether there ever was.
405 Method Not Allowed
The address exists; that verb does not work on it.
406 Not Acceptable
Nothing can be produced that matches the Accept header.
408 Request Timeout
The client took too long to send it.
409 Conflict
It clashes with the current state — an edit against a stale version.
410 Gone
It was here and is deliberately gone. Stronger than 404.
413 Payload Too Large
The body is bigger than the server will take.
415 Unsupported Media Type
The Content-Type is not one this endpoint reads.
418 I'm a teapot
A 1998 April Fools joke, in the standard, still implemented for fun.
422 Unprocessable Content
Well formed, but the data fails validation. The one people want when they reach for 400.
425 Too Early
Refusing a replayable request sent in TLS early data.
428 Precondition Required
Send an If-Match so you do not overwrite somebody blindly.
429 Too Many Requests
Rate limited. Retry-After says how long to wait.
431 Request Header Fields Too Large
Usually one enormous cookie.
451 Unavailable For Legal Reasons
Blocked by law. The number is a Fahrenheit 451 joke.
500 Internal Server Error
Something threw. The catch-all, and a sign nothing more specific was chosen.
501 Not Implemented
The server does not support that method at all.
502 Bad Gateway
A proxy got nonsense from upstream. Usually the app behind it is down.
503 Service Unavailable
Temporarily down or overloaded; Retry-After may say when.
504 Gateway Timeout
A proxy waited for upstream and gave up.
507 Insufficient Storage
No room to hold what was sent.ファイルは端末の外に出ません
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使い方
- 空のままにするとクラスごとの一覧が出ます。
- 番号を入れるとその1件が出ます。
- 4xxと入れるとそのクラス全体が出ます。
- 「キャッシュ」「リダイレクト」のような言葉でも探せます。
よくある質問
- 401と403はどう違いますか？
- 401は「あなたが誰か分からない」——認証してやり直してください。403は「誰かは分かっている、その上で駄目です」。401の名前がUnauthorized（認可されていない）なのに意味は未認証なので、逆に使われ続けています。
- 400と422はどちらを返すべきですか？
- 400はリクエストそのものが壊れているとき——JSONが不正、ヘッダが足りない。422は構文としては読めたが内容が検証に通らないときです。多くの人が400を使う場面は、実際には422です。
- 418とは何ですか？
- 1998年のエイプリルフールのジョークですが、実在のRFCに載っていて実装もされており、削除の提案が出ては却下されています。意味は「私はティーポットです」。
- リダイレクトはどれを使えばいいですか？
- 恒久的に移転し検索エンジンにも移してほしいなら301、一時的なら302です。POSTがGETに変わっては困る場合は308と307を使います。この2つはそのためだけに存在します。
- サーバーに送信されますか？
- いいえ。ブラウザの中だけで動くので、入力した内容はお使いのパソコンから出ません。