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List of HTTP headers

Posted by Viral Sarvaiya on November 13, 2009

HTTP Headers form the core of an HTTP request, and are very important in an HTTP response. They define various characteristics of the data that is requested or the data that has been provided. The headers are separated from the request or response body by a blank line. HTTP headers can be near-arbitrary strings, but only some are commonly understood.

Requests

Header Description Example
Accept Content-Types that are acceptable Accept: text/plain
Accept-Charset Character sets that are acceptable Accept-Charset: iso-8859-5
Accept-Encoding Acceptable encodings Accept-Encoding: compress, gzip
Accept-Language Acceptable languages for response Accept-Language: da
Accept-Ranges Allows the server to indicate its acceptance of range requests for a resource Accept-Ranges: bytes
Authorization Authentication credentials for HTTP authentication Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
Cache-Control Used to specify directives that MUST be obeyed by all caching mechanisms along the request/response chain Cache-Control: no-cache
Connection What type of connection the user-agent would prefer Connection: close
Cookie an HTTP cookie previously sent by the server with Set-Cookie (below) Cookie: $Version=1; UserId=JohnDoe
Content-Length The length of the request body in octets (8-bit bytes) Content-Length: 348
Content-Type The mime type of the body of the request (used with POST and PUT requests) Content-Type: application/x-www-form-urlencoded
Date The date and time that the message was sent Date: Tue, 15 Nov 1994 08:12:31 GMT
Expect Indicates that particular server behaviors are required by the client Expect: 100-continue
From The email address of the user making the request From: user@email.com
Host The domain name of the server (for virtual hosting), mandatory since HTTP/1.1 Host: en.wikipedia.org
If-Match Only perform the action if the client supplied entity matches the same entity on the server. This is mainly for methods like PUT to only update a resource if it has not been modified since the user last updated it. If-Match: "737060cd8c284d8af7ad3082f209582d"
If-Modified-Since Allows a 304 Not Modified to be returned if content is unchanged If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
If-None-Match Allows a 304 Not Modified to be returned if content is unchanged, see HTTP ETag If-None-Match: "737060cd8c284d8af7ad3082f209582d"
If-Range If the entity is unchanged, send me the part(s) that I am missing; otherwise, send me the entire new entity If-Range: "737060cd8c284d8af7ad3082f209582d"
If-Unmodified-Since Only send the response if the entity has not been modified since a specific time. If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
Max-Forwards Limit the number of times the message can be forwarded through proxies or gateways. Max-Forwards: 10
Pragma Implementation-specific headers that may have various effects anywhere along the request-response chain. Pragma: no-cache
Proxy-Authorization Authorization credentials for connecting to a proxy. Proxy-Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
Range Request only part of an entity. Range: bytes=500-999
Referer This is the address of the previous web page from which a link to the currently requested page was followed. Referer: http://en.wikipedia.org/wiki/Main_Page
TE The transfer encodings the user agent is willing to accept: the same values as for the response header Transfer-Encoding can be used, plus the “trailers” value (related to the “chunked” transfer method) to notify the server it accepts to receive additional headers (the trailers) after the last, zero-sized, chunk. TE: trailers, deflate;q=0.5
Upgrade Ask the server to upgrade to another protocol. Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
User-Agent The user agent string of the user agent User-Agent: Mozilla/5.0 (Linux; X11)
Via Informs the server of proxies through which the request was sent. Via: 1.0 fred, 1.1 nowhere.com (Apache/1.1)
Warn A general warning about possible problems with the entity body. Warn: 199 Miscellaneous warning

Responses

Header Description Example
Accept-Ranges What partial content range types this server supports Accept-Ranges: bytes
Age The age the object has been in a proxy cache in seconds Age: 12
Allow Valid actions for a specified resource. To be used for a 405 Method not allowed Allow: GET, HEAD
Cache-Control Tells all caching mechanisms from server to client whether they may cache this object Cache-Control: no-cache
Content-Encoding The type of encoding used on the data Content-Encoding: gzip
Content-Language The language the content is in Content-Language: da
Content-Length The length of the response body in octets (8-bit bytes) Content-Length: 348
Content-Location An alternate location for the returned data Content-Location: /index.htm
Content-Disposition An opportunity to raise a “File Download” dialogue box for a known MIME type Content-Disposition: attachment; filename=fname.ext
Content-MD5 A Base64-encoded binary MD5 sum of the content of the response Content-MD5: Q2hlY2sgSW50ZWdyaXR5IQ==
Content-Range Where in a full body message this partial message belongs Content-Range: bytes 21010-47021/47022
Content-Type The mime type of this content Content-Type: text/html; charset=utf-8
Date The date and time that the message was sent Date: Tue, 15 Nov 1994 08:12:31 GMT
ETag An identifier for a specific version of a resource, often a Message Digest, see ETag ETag: "737060cd8c284d8af7ad3082f209582d"
Expires Gives the date/time after which the response is considered stale Expires: Thu, 01 Dec 1994 16:00:00 GMT
Last-Modified The last modified date for the requested object, in RFC 2822 format Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
Location Used in redirection, or when a new resource has been created. Location: http://www.w3.org/pub/WWW/People.html
Pragma Implementation-specific headers that may have various effects anywhere along the request-response chain. Pragma: no-cache
Proxy-Authenticate Request authentication to access the proxy. Proxy-Authenticate: Basic
Refresh Used in redirection, or when a new resource has been created. This refresh redirects after 5 seconds.
(This is a proprietary/non-standard header extension introduced by Netscape and supported by most web browsers.)
Refresh: 5; url=http://www.w3.org/pub/WWW/People.html
Retry-After If an entity is temporarily unavailable, this instructs the client to try again after a specified period of time. Retry-After: 120
Server A name for the server Server: Apache/1.3.27 (Unix) (Red-Hat/Linux)
Set-Cookie an HTTP cookie Set-Cookie: UserID=JohnDoe; Max-Age=3600; Version=1
Trailer The Trailer general field value indicates that the given set of header fields is present in the trailer of a message encoded with chunked transfer-coding. Trailer: Max-Forwards
Transfer-Encoding The form of encoding used to safely transfer the entity to the user. Currently defined methods are: chunked, compress, deflate, gzip, identity. Transfer-Encoding: chunked
Vary Tells downstream proxies how to match future request headers to decide whether the cached response can be used rather than requesting a fresh one from the origin server. Vary: *
Via Informs the client of proxies through which the response was sent. Via: 1.0 fred, 1.1 nowhere.com (Apache/1.1)
Warning A general warning about possible problems with the entity body. Warning: 199 Miscellaneous warning
WWW-Authenticate Indicates the authentication scheme that should be used to access the requested entity. WWW-Authenticate: Basic
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3 Responses to “List of HTTP headers”

  1. Cloak Url said

    Header is also required; digit HTTP response code, followed by a textual message. Cloak Url

  2. QFDaniel said

    Actually,good post. thx

  3. When a new value is merged onto an existing header it is separated from the existing header with a comma. Url Cloaking

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