Content-Types that are acceptable for the response, e.g. Accept: text/plain

Character sets that are acceptable, e.g. Accept-Charset: utf-8

Acceptable version in time, e.g. Accept-Datetime: Thu, 31 May 2007 20:35:00 GMT

List of acceptable encodings. See HTTP compression. e.g. Accept-Encoding: gzip, deflate

List of acceptable human languages for response, e.g. Accept-Language: en-US

What partial content range types this server supports, e.g. Accept-Ranges: bytes

Specifying which web sites can participate in cross-origin resource sharing, e.g. Access-Control-Allow-Origin: *

The age the object has been in a proxy cache in seconds, e.g. Age: 12

Valid actions for a specified resource. To be used for a 405 Method not allowed. e.g. Allow: GET, HEAD

Authentication credentials for HTTP authentication, e.g. Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==

Tells all caching mechanisms from server to client or vice-versa whether they may cache this object. It is measured in seconds. e.g. Cache-Control: no-cache e.g. Cache-Control: max-age=3600

Options that are desired for the connection, e.g. Connection: keep-alive e.g. Connection: close

An opportunity to raise a "File Download" dialogue box for a known MIME type with binary format or suggest a filename for dynamic content. Quotes are necessary with special characters. e.g. Content-Disposition: attachment; filename="fname.ext"

The type of encoding used on the data. See HTTP compression. e.g. Content-Encoding: gzip

The language the content is in, e.g. Content-Language: da

The length of the request/response body in octets (8-bit bytes) Content-Length: 348

An alternate location for the returned data Content-Location: /index.htm

A Base64-encoded binary MD5 sum of the content of the response, e.g. Content-MD5: Q2hlY2sgSW50ZWdyaXR5IQ==

Where in a full body message this partial message belongs, e.g. Content-Range: bytes 21010-47021/47022

The MIME type of this content (requests use this only with POST / PUT methods), e.g. Content-Type: application/x-www-form-urlencoded e.g. Content-Type: text/html; charset=utf-8

An HTTP cookie previously sent by the server with Set-Cookie (below), e.g. Cookie: $Version=1; Skin=new;

The date and time that the message was sent, e.g. Date: Tue, 15 Nov 1994 08:12:31 GMT

An identifier for a specific version of a resource, often a message digest, e.g. ETag: "737060cd8c284d8af7ad3082f209582d"

Indicates that particular server behaviors are required by the client, e.g. Expect: 100-continue

Gives the date/time after which the response is considered stale, e.g. Expires: Thu, 01 Dec 1994 16:00:00 GMT

The email address of the user making the request, e.g. From: user@example.com

The domain name of the server (for virtual hosting), and the TCP port number on which the server is listening. The port number may be omitted if the port is the standard port for the service requested. Mandatory since HTTP/1.1. Although domain name are specified as case-insensitive, it is not specified whether the contents of the Host field should be interpreted in a case-insensitive manner and in practice some implementations of virtual hosting interpret the contents of the Host field in a case-sensitive manner. e.g. Host: en.wikipedia.org:80

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. e.g. If-Match: "737060cd8c284d8af7ad3082f209582d"

Allows a 304 Not Modified to be returned if content is unchanged, e.g. If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT

Allows a 304 Not Modified to be returned if content is unchanged, see HTTP ETag, e.g. If-None-Match: "737060cd8c284d8af7ad3082f209582d"

If the entity is unchanged, send me the part(s) that I am missing; otherwise, send me the entire new entity. e.g. If-Range: "737060cd8c284d8af7ad3082f209582d"

Only send the response if the entity has not been modified since a specific time, e.g. If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT

The last modified date for the requested object, in RFC 2822 format e.g. Last-Modified: Tue, 15 Nov 1994 12:45:26 +0000

Used to express a typed relationship with another resource, where the relation type is defined by RFC 5988 e.g. Link: </feed>; rel="alternate"

Used in redirection, or when a new resource has been created. e.g. Location: http://www.w3.org/pub/WWW/People.html

Limit the number of times the message can be forwarded through proxies or gateways, e.g. Max-Forwards: 10

Initiates a request for cross-origin resource sharing (asks server for an 'Access-Control-Allow-Origin' response header), e.g. Origin: http://www.example-social-network.com

This header is supposed to set P3P policy, in the form of P3P:CP="your_compact_policy". However, P3P did not take off, most browsers have never fully implemented it, a lot of websites set this header with fake policy text, that was enough to fool browsers the existence of P3P policy and grant permissions for third party cookies. e.g. P3P: CP="This is not a P3P policy! See ... for more info."

Implementation-specific headers that may have various effects anywhere along the request-response chain. e.g. Pragma: no-cache

Request authentication to access the proxy. e.g. Proxy-Authenticate: Basic

Authorization credentials for connecting to a proxy, e.g. Proxy-Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==

Request only part of an entity. Bytes are numbered from 0. e.g. Range: bytes=500-999

This is the address of the previous web page from which a link to the currently requested page was followed. (The word referrer is misspelled in the RFC as well as in most implementations.), e.g. Referer: http://en.wikipedia.org/wiki/Main_Page

Used in redirection, or when a new resource has been created. This refresh redirects after 5 seconds. e.g. Refresh: 5; url=http://www.w3.org/pub/WWW/People.html

If an entity is temporarily unavailable, this instructs the client to try again after a specified period of time (seconds). e.g. Retry-After: 120

A name for the server, e.g. Server: Apache/2.4.1 (Unix)

An HTTP cookie, e.g. Set-Cookie: UserID=JohnDoe; Max-Age=3600; Version=1

The HTTP status of the response. "Status" is not listed as a registered header. The "Status-Line" of a "Response" is defined by RFC2616 without any explicit Status: header name. e.g. Status: 200 OK

A HSTS Policy informing the HTTP client how long to cache the HTTPS only policy and whether this applies to subdomains. e.g. Strict-Transport-Security: max-age=16070400; includeSubDomains

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 expects to receive additional headers (the trailers) after the last, zero-sized, chunk. e.g. TE: trailers, deflate

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. e.g. Trailer: Max-Forwards

The form of encoding used to safely transfer the entity to the user. Currently defined methods are: chunked, compress, deflate, gzip, identity. e.g. Transfer-Encoding: chunked

Ask the server to upgrade to another protocol. e.g. Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11

The user agent string of the user agent, e.g. User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20100101 Firefox/21.0

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. e.g. Vary: *

Informs the client or server of proxies through which the response / request was sent. e.g. Via: 1.0 fred, 1.1 example.com (Apache/1.1)

A general warning about possible problems with the entity body. e.g. Warning: 199 Miscellaneous warning

Indicates the authentication scheme that should be used to access the requested entity. e.g. WWW-Authenticate: Basic