HTTPヘッダーリファレンス
HTTPリクエスト・レスポンスヘッダーの完全なリファレンスです。
33 headers
Media types the client can process (e.g. application/json, text/html).
Accept: text/html,application/xhtml+xmlContent encodings the client supports (gzip, deflate, br).
Accept-Encoding: gzip, deflate, brPreferred natural languages for the response.
Accept-Language: en-US,en;q=0.9Credentials for HTTP authentication.
Authorization: Bearer eyJhbGc...Directives for caching mechanisms in both requests and responses.
Cache-Control: no-cache, no-storeControl options for the current connection.
Connection: keep-aliveSize of the request/response body in bytes.
Content-Length: 348Media type of the request/response body.
Content-Type: application/json; charset=utf-8HTTP cookies previously sent by the server.
Cookie: session=abc123; user=johnDomain name and port of the server. Required in HTTP/1.1.
Host: www.example.com:443Makes the request conditional; returns 304 if not modified.
If-Modified-Since: Mon, 18 Jul 2016 02:36:04 GMTMakes request conditional using ETags.
If-None-Match: "737060cd8c284d8af7ad3082f209582d"The origin that initiated the request (for CORS).
Origin: https://developer.example.comAddress of the previous web page that linked to the current page.
Referer: https://developer.example.com/pageApplication, OS, vendor, and version of the requesting client.
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64)Indicates whether the response can be shared with code from the given origin.
Access-Control-Allow-Origin: *HTTP methods allowed when accessing the resource for CORS.
Access-Control-Allow-Methods: GET, POST, PUTHeaders that can be used during the actual CORS request.
Access-Control-Allow-Headers: Content-Type, AuthorizationEncoding applied to the response body (gzip, br, etc.).
Content-Encoding: gzipControls resources the user agent is allowed to load.
Content-Security-Policy: default-src 'self'Identifier for a specific version of a resource (for caching).
ETag: "33a64df551425fcc55e4d42a148795d9f25f89d4"Date/time after which the response is considered stale.
Expires: Thu, 01 Dec 2025 16:00:00 GMTDate/time when the resource was last modified.
Last-Modified: Wed, 21 Oct 2015 07:28:00 GMTURL to redirect to for 3xx responses or the URL of the newly created resource.
Location: /new-pageHow long to wait before making another request (rate limiting/503).
Retry-After: 120Send a cookie from the server to the user agent.
Set-Cookie: id=a3fWa; Expires=Thu, 21 Oct 2025 07:28:00 GMT; Secure; HttpOnlyForce HTTPS for all future connections (HSTS).
Strict-Transport-Security: max-age=31536000; includeSubDomainsForm of encoding used to safely transfer the payload body.
Transfer-Encoding: chunkedDetermines which request headers to use for cache key.
Vary: Accept-Encoding, Accept-LanguageAuthentication method to access the resource (sent with 401).
WWW-Authenticate: Basic realm="Access to staging site"Prevent MIME type sniffing.
X-Content-Type-Options: nosniffIndicate whether the response can be framed (clickjacking protection).
X-Frame-Options: DENYEnable XSS filtering in older browsers (deprecated, use CSP instead).
X-XSS-Protection: 1; mode=blockこのツールについて
The HTTP Headers Reference covers the most commonly used request and response headers with plain-English descriptions and example values. Security-critical headers are highlighted in red.
Filter by category (Request, Response, or Both) or search by header name and keyword to quickly find what you need.
使い方
- Type a header name or keyword in the search box to filter the list instantly.
- Use the category dropdown to show only Request, Response, or Both headers.
- Each entry shows the header name, category badge, description, and an example value.
- Use the example values as a starting point when configuring your server or HTTP client.
活用事例
Back-end engineers set correct security headers (CSP, HSTS, X-Frame-Options) before deployment. Front-end developers debug CORS issues using the Access-Control headers. Students learning HTTP use the reference to understand how the protocol works.
よくある質問
- What is the difference between request and response headers? — Request headers are sent by the client to provide context (accepted types, authentication). Response headers are sent by the server with metadata about the response (content type, caching, security).
- Which headers should every site add for security? — At minimum: Strict-Transport-Security, Content-Security-Policy, X-Content-Type-Options, and X-Frame-Options on all responses.
- Are all HTTP headers listed here? — No. This reference focuses on the most commonly used standard and security headers. For a complete list see the MDN HTTP headers documentation.