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| Header | Explanation | Example |
|---|---|---|
| Accept | The content types the client can accept | Accept: text/plain, text/html |
| Accept-Charset | The character sets the browser can accept. | Accept-Charset: iso-8859-5 |
| Accept-Encoding | Specifies the content compression encodings the browser supports for responses returned by the web server. | Accept-Encoding: compress, gzip |
| Accept-Language | Languages accepted by the browser | Accept-Language: en,zh |
| Accept-Ranges | Can request one or more sub-range fields of a web page entity | Accept-Ranges: bytes |
| Authorization | Authorization credentials for HTTP authentication | Authorization: authorization credentials |
| Cache-Control | The caching mechanism the request and response follow | Cache-Control: no-cache |
| Connection | Indicates whether a persistent connection is required. (HTTP 1.1 uses persistent connections by default) | Connection: close |
| Cookie | When an HTTP request is sent, all cookie values stored under the requested domain are sent to the web server too. | Cookie: $Version=1; Skin=new; |
| Content-Length | Length of requested content | Content-Length: 348 |
| Content-Type | The MIME information of the requested entity | Content-Type: application/x-www-form-urlencoded |
| Date | Date and time the request was sent | Date: Tue, 15 Nov 2010 08:12:31 GMT |
| Expect | Requests specific server behavior | Expect: 100-continue |
| From | Email of the user making the request | From: user@jsons.cn |
| Host | The domain and port of the requested server | Host: www.jsons.cn |
| If-Match | Only valid if the request content matches the entity | If-Match: "specific value" |
| If-Modified-Since | The request succeeds if the requested part was modified after the specified time; otherwise a 304 code is returned | If-Modified-Since: Sat, 29 Oct 2010 19:43:31 GMT |
| If-None-Match | Returns 304 if the content has not changed; the parameter is the Etag previously sent by the server, compared with the Etag in the server's response to judge whether it changed | If-None-Match: "specific value" |
| If-Range | If the entity has not changed, the server sends the part the client lost; otherwise it sends the whole entity. Also uses Etag | If-Range: "specific value" |
| If-Unmodified-Since | The request succeeds only if the entity has not been modified after the specified time | If-Unmodified-Since: Sat, 29 Oct 2010 19:43:31 GMT |
| Max-Forwards | Limits the time information takes to pass through proxies and gateways | Max-Forwards: 10 |
| Pragma | Used to include implementation-specific directives | Pragma: no-cache |
| Proxy-Authorization | Authorization certificate for connecting to the proxy | Proxy-Authorization: credentials for connecting to a proxy |
| Range | Request only part of an entity, specifying a range | Range: bytes=500-999 |
| Referer | The address of the previous page from which the current request followed, i.e. the referrer | Referer: http://www.jsons.cn |
| TE | The transfer encoding the client is willing to accept; notifies the server of the accepted trailer headers | TE: trailers,deflate;q=0.5 |
| Upgrade | Specifies a transfer protocol to the server so that it performs the conversion (if supported) | Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11 |
| User-Agent | The User-Agent content includes information about the user making the request | User-Agent: Mozilla/5.0 (Linux; X11) |
| Via | Notifies the intermediate gateway or proxy server address, communication protocol | Via: 1.0 fred, 1.1 nowhere.com (Apache/1.1) |
| Warning | Warning information about the message entity | Warn: 199 Miscellaneous warning |
| Header | Explanation | Example |
|---|---|---|
| Accept-Ranges | Indicates whether the server supports the specified range request and which types of segmented requests | Accept-Ranges: bytes |
| Age | The estimated time formed from the origin server to the proxy cache (in seconds, non-negative) | Age: 12 |
| Allow | A valid request behavior for a network resource; returns 405 if not allowed | Allow: GET, HEAD |
| Cache-Control | Tells all caching mechanisms whether they may cache and which type | Cache-Control: no-cache |
| Content-Encoding | The content-compression encoding types supported by the web server for returned content. | Content-Encoding: gzip |
| Content-Language | Response language | Content-Language: en,zh |
| Content-Length | Response length | Content-Length: 348 |
| Content-Location | An alternate address for the requested resource | Content-Location: /index.htm |
| Content-MD5 | Returns the MD5 checksum of the resource | Content-MD5: MD5 checksum value |
| Content-Range | Byte position of this part in the entire response body | Content-Range: bytes 21010-47021/47022 |
| Content-Type | Returns the MIME type of the content | Content-Type: text/html; charset=utf-8 |
| Date | Time the message was sent from the origin server | Date: Tue, 15 Nov 2010 08:12:31 GMT |
| ETag | Current value of the entity tag of the request variable | ETag: "current value of the entity tag for the requested variant" |
| Expires | Date and time the response expires | Expires: Thu, 01 Dec 2010 16:00:00 GMT |
| Last-Modified | Last modification time of the requested resource | Last-Modified: Tue, 15 Nov 2010 12:45:26 GMT |
| Location | Used to redirect the recipient to a location other than the requested URL to complete the request or identify a new resource | Location: http://www.jsons.cn |
| Pragma | Includes implementation-specific directives that can be applied to any recipient in the response chain | Pragma: no-cache |
| Proxy-Authenticate | It indicates the authentication scheme and parameters applicable to the proxy for this URL | Proxy-Authenticate: Basic |
| refresh | Applied to a redirect or a newly created resource, redirects after 5 seconds (proposed by Netscape, supported by most browsers) |
Refresh: 5; url= http://www.jsons.cn
|
| Retry-After | If the entity is temporarily unavailable, tell the client to try again after the specified time | Retry-After: 120 |
| Server | Web server software name | Server: Apache/1.3.27 (Unix) (Red-Hat/Linux) |
| Set-Cookie | Set Http Cookie | Set-Cookie: UserID=JohnDoe; Max-Age=3600; Version=1 |
| Trailer | Indicates the header field is present at the end of the chunked transfer encoding | Trailer: Max-Forwards |
| Transfer-Encoding | File transfer encoding | Transfer-Encoding:chunked |
| Vary | Tells downstream proxies whether to use a cached response or request from the origin server | Vary: * |
| Via | Tells the proxy from where the response was sent | Via: 1.0 fred, 1.1 nowhere.com (Apache/1.1) |
| Warning | Warns of possible entity problems | Warning: 199 Miscellaneous warning |
| WWW-Authenticate | Indicates the authorization scheme the client should use for the requested entity | WWW-Authenticate: Basic |
HTTP headers provide information about a request, a response or other sent entities. HTTP headers include four parts: general headers, request headers, response headers and entity headers.
Each header field consists of a field name, a colon (:) and a field value
General header: usable in both requests and responses; associated with the transaction as a whole rather than a specific resource
Request header: allows the client to pass information about itself and the desired response form
Response header: server and response for passing its own information
Entity header: defines information about the transferred resource; usable for both requests and responses
This tool belongs to the “Reference tables” category.
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Some lookups expose a JSON endpoint; the full list is on the Network Tools → API reference page.
Specifications evolve. These pages list the common entries and note the last update — report anything wrong.
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