什么是HTTP标头，为什么它们很重要？

HTTP标头是随每个HTTP请求和响应发送的键值对。它们携带有关通信的元数据：认证凭据、内容类型、缓存指令、CORS策略、cookie等。标头允许服务器和客户端协商数据交换方式，而无需在URL或正文中编码所有内容。

请求标头和响应标头有什么区别？

请求标头由客户端（浏览器/应用）发送到服务器——例如：Accept、Authorization、Content-Type、Cookie。响应标头由服务器发回客户端——例如：Set-Cookie、Cache-Control、Content-Encoding、Location。某些标头（如Content-Type）在两个方向都有效。

Content-Type标头用于什么？

Content-Type声明请求或响应正文的媒体类型。例如，JSON数据的`application/json`，HTML页面的`text/html`，文件上传的`multipart/form-data`。服务器用它正确解析正文；浏览器用它适当渲染内容。Content-Type不匹配是API错误的常见原因。

什么是CORS标头，为什么它们很重要？

CORS（跨源资源共享）标头控制网页是否可以向不同域发出请求。关键标头：`Access-Control-Allow-Origin`（哪些源可以访问）、`Access-Control-Allow-Methods`（允许的HTTP方法）、`Access-Control-Allow-Headers`（允许的自定义标头）。没有适当的CORS标头，浏览器会出于安全原因阻止跨源请求。

Authorization标头是什么，结构如何？

Authorization标头携带HTTP认证的凭据。常见方案：基本认证的`Basic base64(user:password)`，OAuth 2.0/JWT令牌的`Bearer `，摘要认证的`Digest`。格式始终为`Authorization: `。此标头通常在每个需要认证的API请求中设置。

HTTP 标头参考

可搜索的 HTTP 请求和响应标头参考表。

头部	类型	分类	描述
Accept	Request	Content Negotiation	Media types acceptable for the response (e.g. text/html, application/json).
Accept-Charset	Request	Content Negotiation	Character sets acceptable for the response.
Accept-Encoding	Request	Content Negotiation	Encoding algorithms the client supports (e.g. gzip, deflate, br).
Accept-Language	Request	Content Negotiation	Natural languages preferred for the response (e.g. en-US, fr).
Authorization	Request	Authentication	Credentials for authenticating the client with the server (e.g. Bearer token).
Cookie	Request	State	HTTP cookies previously set by the server, sent back with each request.
Expect	Request	Request Control	Indicates that particular server behaviors are required by the client (e.g. 100-continue).
Host	Request	Request Target	Domain name and port number of the server being addressed. Required in HTTP/1.1.
If-Match	Request	Conditional	Makes the request conditional based on matching ETag values.
If-Modified-Since	Request	Conditional	Makes the request conditional based on modification date.
If-None-Match	Request	Conditional	Makes the request conditional based on non-matching ETag values.
If-Unmodified-Since	Request	Conditional	Makes the request conditional on the resource not being modified since the given date.
Origin	Request	CORS	Indicates the origin from which the cross-site request is initiated.
Proxy-Authorization	Request	Authentication	Credentials for authenticating with a proxy server.
Range	Request	Partial Requests	Requests only part of a resource (e.g. bytes=0-1023 for the first 1 KB).
Referer	Request	Request Context	URL of the page from which the request originated.
TE	Request	Transfer Encoding	Specifies transfer encodings the client is willing to accept.
User-Agent	Request	Request Context	Contains information about the client software making the request.
X-Forwarded-For	Request	Proxies	Identifies the originating IP address when the request passes through proxies.
X-Requested-With	Request	Custom	Commonly used to identify Ajax requests (value: XMLHttpRequest).
Accept-Ranges	Response	Partial Requests	Indicates if the server supports range requests (bytes or none).
Age	Response	Caching	Time in seconds the object has been stored in a proxy cache.
Allow	Response	Request Methods	HTTP methods allowed for the requested resource (used in 405 responses).
Content-Disposition	Response	Response Body	Indicates whether content should be displayed inline or as a file download.
Content-Encoding	Response	Response Body	Encoding applied to the response body (e.g. gzip, br).
Content-Language	Response	Content Negotiation	Natural language(s) of the response body.
Content-Length	Response	Response Body	Size of the response body in bytes.
Content-Range	Response	Partial Requests	Indicates the range of bytes sent in a partial content response (206).
ETag	Response	Caching	Unique identifier for the specific version of a resource; used for cache validation.
Expires	Response	Caching	Date/time after which the response is considered stale.
Last-Modified	Response	Caching	Date and time the resource was last modified on the server.
Location	Response	Redirects	URL to redirect the client to in 3xx or 201 responses.
Proxy-Authenticate	Response	Authentication	Defines the authentication method to use for a proxy (407 response).
Retry-After	Response	Request Control	How long to wait before making a new request after a 429 or 503 response.
Server	Response	Server Info	Software information about the origin server.
Set-Cookie	Response	State	Sends a cookie from the server to the client for storage.
Strict-Transport-Security	Response	Security	HSTS: forces browsers to use HTTPS for subsequent requests.
Vary	Response	Caching	Tells caches which request headers to use as cache keys.
WWW-Authenticate	Response	Authentication	Defines the authentication method for accessing the resource (401 response).
X-Content-Type-Options	Response	Security	Prevents MIME sniffing. Use value: nosniff.
X-Frame-Options	Response	Security	Controls whether the page can be embedded in an iframe (DENY, SAMEORIGIN).
X-XSS-Protection	Response	Security	Enables XSS filtering in older browsers (legacy, mostly deprecated).
Cache-Control	Both	Caching	Directives for caching in requests and responses (e.g. no-cache, max-age=3600).
Connection	Both	Connection Management	Controls whether the network connection stays open (keep-alive or close).
Content-Type	Both	Response Body	Media type of the request or response body (e.g. application/json).
Date	Both	Timestamps	Date and time the message was sent.
Pragma	Both	Caching	Legacy cache control directive (no-cache). Superseded by Cache-Control.
Trailer	Both	Transfer Encoding	Indicates which headers will be present in the trailer of a chunked response.
Transfer-Encoding	Both	Transfer Encoding	Encoding applied to the message body for transfer (e.g. chunked).
Via	Both	Proxies	Added by proxies to indicate intermediate protocols and recipients.
Warning	Both	Request Control	General warnings about possible problems with the message (deprecated in RFC 9110).
Access-Control-Allow-Origin	Response	CORS	Specifies which origins are allowed for CORS requests.
Access-Control-Allow-Methods	Response	CORS	HTTP methods allowed for CORS preflight responses.
Access-Control-Allow-Headers	Response	CORS	HTTP headers allowed in CORS preflight responses.
Access-Control-Allow-Credentials	Response	CORS	Indicates if the response can be shared when credentials are included.
Access-Control-Max-Age	Response	CORS	How long the preflight response can be cached (in seconds).
Cross-Origin-Opener-Policy	Response	Security	Controls the browsing context group for cross-origin documents.
Cross-Origin-Resource-Policy	Response	Security	Prevents cross-origin reads of the response in certain contexts.
Content-Security-Policy	Response	Security	Specifies allowed sources for content types to prevent XSS and injection attacks.
Referrer-Policy	Response	Security	Controls how much referrer information is sent with requests.
Permissions-Policy	Response	Security	Controls browser features and APIs that are allowed to be used (formerly Feature-Policy).

关于此工具

HTTP 头部是随附于每个网络请求和响应的元数据字段，控制着从缓存行为到身份验证和内容协商的一切。HTTP Headers Reference 是一份关于现代网络开发中最常见和最重要的头部的可搜索指南，帮助开发人员快速理解每个头部的作用、接受的值以及何时使用它。

只需搜索头部名称或浏览分类列表，即可找到其目的、语法和典型用例的详细信息。无论是调试 CORS 错误、配置缓存控制、设置安全策略还是理解重定向行为，这份参考资料都能直击要点，为您提供所需的准确信息，无需离开此页面。

此工具对后端开发人员、前端工程师、DevOps 专业人员和任何管理 HTTP 基础设施的人员都至关重要。它完全在浏览器中运行，无需服务器调用，在构建 API、配置网络服务器或排查生产环境中的请求头问题时，提供快速且私密的离线参考。

常见问题

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