60 ステータスコード
The server has received the request headers and the client should proceed to send the request body.
ユースケース: Large file uploads — client sends Expect: 100-continue before body.
The server agrees to switch protocols as requested by the client.
ユースケース: WebSocket upgrades: HTTP → WebSocket.
The server has received and is processing the request, but no response is yet available.
ユースケース: Long-running WebDAV operations to prevent client timeout.
Returns response headers before the final response, allowing the client to preload resources.
ユースケース: Preloading critical CSS/JS while the server prepares the full response.
The request has succeeded. The response body contains the requested resource.
ユースケース: Standard successful GET, POST, PUT, PATCH responses.
The request has been fulfilled and a new resource has been created.
ユースケース: Successful POST that creates a resource. Include Location header pointing to new resource.
The request has been accepted for processing but processing has not been completed.
ユースケース: Async operations: email sending, report generation, batch jobs.
The response is successful but the information was obtained from a third-party source.
ユースケース: Proxies or mirrors that transform the original response.
The server successfully processed the request but returns no content.
ユースケース: DELETE operations, form submissions with no redirect, successful PATCH with no body needed.
The server successfully processed the request and asks the client to reset the document view.
ユースケース: Forms — server wants the client to clear the form after submission.
The server is delivering only part of the resource due to a range header sent by the client.
ユースケース: Video streaming, resumable file downloads, pagination of large binary resources.
The response body contains status information for multiple independent operations.
ユースケース: WebDAV batch operations where each sub-request has its own status.
Members of a DAV binding have already been enumerated in a previous reply.
ユースケース: WebDAV — avoids re-listing resources already returned.
The server has fulfilled a GET for the resource and the response represents the result of one or more instance manipulations.
ユースケース: HTTP delta encoding — differential responses for caching efficiency.
The request has more than one possible response. The user should choose one.
ユースケース: Content negotiation — multiple formats or languages available.
The resource has been permanently moved to a new URL. Future requests should use the new URL.
ユースケース: Site migration, domain changes. Passes full SEO link equity to new URL.
The resource is temporarily at a different URL. Client should continue using original URL.
ユースケース: Temporary maintenance pages, A/B testing redirects.
The server directs the client to get the requested resource at another URI using a GET request.
ユースケース: Post/Redirect/Get pattern — after a successful POST, redirect to a confirmation page.
The resource has not been modified since the last request. Client should use its cached version.
ユースケース: Conditional GET with If-None-Match or If-Modified-Since. Saves bandwidth.
The resource is temporarily at a different URL. The method and body must not change.
ユースケース: Like 302, but guarantees the HTTP method is preserved on redirect.
The resource has permanently moved. The method and body must not change.
ユースケース: Like 301 but method-preserving. Good for migrating POST endpoints.
The server cannot process the request due to client error (malformed syntax, invalid parameters).
ユースケース: Invalid JSON body, missing required fields, invalid query params, validation failures.
The client must authenticate itself to get the requested response.
ユースケース: Missing or invalid Bearer token / API key. Should trigger a login prompt.
Reserved for future use; some APIs use it for subscription/paywall responses.
ユースケース: Paywalled API endpoints, exceeded free-tier limits, subscription required.
The client is authenticated but lacks permission to access the resource.
ユースケース: User is logged in but lacks the required role or ownership. Don't reveal resource existence.
The server cannot find the requested resource. The URL may be incorrect or the resource deleted.
ユースケース: Missing pages, deleted resources, invalid IDs. Most common HTTP error.
The HTTP method is not supported for the requested resource.
ユースケース: Calling DELETE on a read-only endpoint. Include Allow header listing valid methods.
The server cannot produce a response matching the Accept headers sent by the client.
ユースケース: Client requests application/xml but only JSON is available.
The client must authenticate itself with the proxy server.
ユースケース: Corporate proxy requiring credentials before passing requests through.
The server timed out waiting for the request.
ユースケース: Client took too long to send the complete request. Server closes the connection.
The request conflicts with the current state of the server.
ユースケース: Duplicate username registration, version conflicts in optimistic concurrency.
The resource is permanently deleted and will not be available again.
ユースケース: Deleted content where you want search engines to deindex permanently.
The server requires a Content-Length header in the request.
ユースケース: API endpoints that need to pre-allocate resources based on expected body size.
The server does not meet a precondition the client specified in its headers.
ユースケース: Optimistic concurrency with If-Match/ETags. Edit conflict detection.
The request body is larger than the server is willing to process.
ユースケース: File upload exceeds limit. Include Retry-After if temporary.
The URI provided was too long for the server to process.
ユースケース: Excessively long query strings, typically from GET requests with too much data.
The media format of the request body is not supported by the server.
ユースケース: Sending XML to an endpoint that only accepts JSON.
The range specified in the Range header cannot be fulfilled.
ユースケース: File download resumed beyond the file's actual size.
The expectation indicated in the Expect header cannot be met by the server.
ユースケース: Client sends Expect: 100-continue but server can't accommodate it.
The server refuses to brew coffee because it's a teapot (RFC 2324 April Fools' joke).
ユースケース: Easter egg in APIs. Some services use it to reject clearly bot-driven requests.
The request was well-formed but failed semantic validation.
ユースケース: JSON is valid but business logic validation fails (e.g., end date before start date).
The resource that is being accessed is locked.
ユースケース: WebDAV — file checked out by another user.
The request failed because it depended on another request that failed.
ユースケース: WebDAV batch operations where a prior step failed.
The server is unwilling to process a request that might be replayed.
ユースケース: TLS 0-RTT early data that could be a replay attack.
The client should switch to a different protocol.
ユースケース: Server requires HTTPS but received HTTP, or requires HTTP/2.
The server requires the request to be conditional to prevent lost updates.
ユースケース: API requires If-Match header for update operations to prevent conflicts.
The user has sent too many requests in a given amount of time (rate limiting).
ユースケース: API rate limits exceeded. Include Retry-After header with wait time.
The server is unwilling to process the request because its header fields are too large.
ユースケース: Excessively large cookies or too many custom headers.
The resource is unavailable due to legal reasons such as government censorship.
ユースケース: GDPR compliance blocking, DMCA takedowns, regional legal restrictions.
The server encountered an unexpected condition that prevented it from fulfilling the request.
ユースケース: Unhandled exceptions, database errors, configuration issues. Generic catch-all.
The server does not support the functionality required to fulfill the request.
ユースケース: HTTP method not recognized or not yet implemented by the server.
The server, while acting as a gateway, received an invalid response from the upstream server.
ユースケース: Upstream API timeout, crashed microservice behind load balancer.
The server is temporarily unable to handle the request due to overload or maintenance.
ユースケース: Planned maintenance, server overload. Include Retry-After header.
The server, acting as a gateway, did not receive a timely response from the upstream server.
ユースケース: Slow database queries, slow microservices causing proxy timeouts.
The HTTP protocol version used in the request is not supported by the server.
ユースケース: Rare — client uses an unsupported HTTP version.
The server has an internal configuration error with transparent content negotiation.
ユースケース: Circular reference in content negotiation configuration.
The server is unable to store the representation needed to complete the request.
ユースケース: WebDAV — disk full. Also used in some APIs for quota exhaustion.
The server detected an infinite loop while processing the request.
ユースケース: WebDAV — infinite loop in directory binding.
Further extensions to the request are required for the server to fulfill it.
ユースケース: HTTP Extension Framework — specific extension policy not met.
The client needs to authenticate to gain network access.
ユースケース: Captive portals — hotel/airport Wi-Fi login pages.
HTTP ステータスコードは、クライアントリクエストに対してウェブサーバーが返す 3 桁の番号です。リクエストが成功、リダイレクト、またはエラーが発生したかを示します。最初の桁がレスポンスクラスを定義します: 1xx（情報）、2xx（成功）、3xx（リダイレクト）、4xx（クライアントエラー）、5xx（サーバーエラー）。
301（永久移動）は、ブラウザと検索エンジンにページが新しい URL に永久的に移動したことを伝え、完全な SEO リンクエクイティを新しい URL に渡します。302（Found / 一時リダイレクト）は一時的な移動を示します。ブラウザはリダイレクトしますが、検索エンジンは通常元の URL をインデックスに保持します。
401 Unauthorized はクライアントが認証されていないことを意味します — 認証情報が提供されていないか、無効です。403 Forbidden はクライアントが認証されているがリソースへのアクセス権限がないことを意味します。ログインを促す場合は 401 を使用し、ユーザーがログインしているが権限がない場合は 403 を使用してください。
リソースを作成する成功した POST の場合、新しいリソースを指す Location ヘッダーとともに 201 Created を返します。リソースを作成せずに処理をトリガーする成功した POST の場合、200 OK を返します。処理が完了していない非同期操作の場合は、202 Accepted を返します。