請求頭和回應頭有什麼差別？

請求頭由客戶端（瀏覽器或應用）發往伺服器；回應頭由伺服器隨答案返回。部分頭如 Content-Type 兩側都可能出現。

HTTP 請求頭名稱區分大小寫嗎？

不區分。依規範名稱大小寫無關，Content-Type 與 content-type 含義相同。Title-Case 僅為約定寫法。

Host 告知伺服器請求指向哪個網域。HTTP/1.1 中必填，使一台伺服器可按名稱託管多個網站。

Cache-Control 規定回應可快取多久；ETag 與 If-None-Match 讓客戶端詢問「內容變了嗎？」，未變則回傳輕量的 304。

HTTP 請求頭是每個請求與回應開頭傳送的鍵值對。它們攜帶內容類型、快取規則、身分認證等中繼資料。本表幫你辨識在建構或除錯網路流量時最常見的請求頭。

更新日期: 2026-09-10

請求頭	方向	用途
Host	request	Identifies the server's host and port (from the URL).
User-Agent	request	Reports the client software (browser, OS, bot) making the request.
Accept	request	Lists the response media types (MIME) the client can handle.
Authorization	request	Carries credentials (token, Basic auth) to authenticate the client.
Content-Type	request/response	States the media type of the request or response body.
Content-Length	request/response	Gives the size in bytes of the request or response body.
Cookie	request	Sends stored key/value pairs from a previous response back to the server.
Set-Cookie	response	Server instructs the client to store a cookie for later requests.
Cache-Control	request/response	Directs caching behaviour: no-cache, max-age, private, etc.
ETag	response	Opaque identifier for a resource version, used for revalidation.
If-None-Match	request	Sends an ETag; server returns 304 if the resource is unchanged.
Location	response	Points the client to a new URL for redirects (3xx) or created resources.
Access-Control-Allow-Origin	response	Permits a browser to share a response across origins (CORS).
X-Forwarded-For	request	Records the client IP as seen through a proxy or load balancer.
Referer	request	Indicates the URL of the page that linked to the requested resource.

請求頭和回應頭有什麼差別？: 請求頭由客戶端（瀏覽器或應用）發往伺服器；回應頭由伺服器隨答案返回。部分頭如 Content-Type 兩側都可能出現。
HTTP 請求頭名稱區分大小寫嗎？: 不區分。依規範名稱大小寫無關，Content-Type 與 content-type 含義相同。Title-Case 僅為約定寫法。
Host 請求頭有什麼用？: Host 告知伺服器請求指向哪個網域。HTTP/1.1 中必填，使一台伺服器可按名稱託管多個網站。
快取如何用請求頭實現？: Cache-Control 規定回應可快取多久；ETag 與 If-None-Match 讓客戶端詢問「內容變了嗎？」，未變則回傳輕量的 304。