List of HTTP header fields

This article lists standard and notable non-standard HTTP header fields.
A core set of fields is standardized by the Internet Engineering Task Force in. The, and are maintained by the IANA. Additional fields may be defined by a web application.
In the past, non-standard header field names were prefixed with X- but this convention was deprecated in June 2012 because of the inconveniences it caused when non-standard fields became standard. An earlier restriction on use of Downgraded- was lifted in March 2013.
A few field values can contain comments, which can be ignored by software.
Many field values may contain a quality key-value pair separated by equals sign, specifying a weight to use in content negotiation. For example, a browser may indicate that it accepts information in German or English, with German as preferred by setting the q value for de higher than that of en, as follows:
Accept-Language: de; q=1.0, en; q=0.5

Request fields

This section lists header fields used in a request.

Standard request fields

A-IM

Acceptable instance-manipulations for the request.
For example: A-IM: feed

Accept

Media type(s) that is/are acceptable for the response. See Content negotiation.
For example: Accept: text/html

Accept-Charset

Character sets that are acceptable.
For example: Accept-Charset: utf-8

Accept-Datetime

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

Accept-Encoding

List of acceptable encodings. See HTTP compression.
For example: Accept-Encoding: gzip, deflate

Accept-Language

List of acceptable human languages for response. See Content negotiation.
For example: Accept-Language: en-US

Access-Control-Request-Method, Access-Control-Request-Headers

Initiates a request for cross-origin resource sharing with Origin.
For example: Access-Control-Request-Method: GET

Authorization

Authentication credentials for HTTP authentication.
For example: Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ

Cache-Control

Used to specify directives that must be obeyed by all caching mechanisms along the request-response chain. Per HTTP/1.1, the no-cache value allows the browser to tell the server and intermediate caches that it wants a fresh version of the resource. The HTTP/1.0, Pragma: no-cache header field has the same purpose.
The behavior of Pragma: no-cache in a response is not specified yet some user agents support it. HTTP/1.1 specifically warns against relying on this behavior.
For example: Cache-Control: no-cache

Connection

Control options for the current connection and list of hop-by-hop request fields.
Must not be used with HTTP/2.
For example: Connection: keep-alive
Connection: Upgrade

Content-Encoding

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

Content-Length

The length of the request body in octets.
For example: Content-Length: 348

Content-MD5

A Base64-encoded binary MD5 sum of the content of the request body.
For example: Content-MD5: Q2hlY2sgSW50ZWdyaXR5IQ

Content-Type

The Media type of the body of the request.
For example: Content-Type: application/x-www-form-urlencoded

Cookie

An HTTP cookie previously sent by the server with Set-Cookie.
For example: Cookie: $Version=1; Skin=new;

Date

The date and time at which the message was originated.
For example: Date: Tue, 15 Nov 1994 08:12:31 GMT

Expect

Indicates that particular server behaviors are required by the client.
For example: Expect: 100-continue

Forwarded

Disclose original information of a client connecting to a web server through an HTTP proxy.
For example: Forwarded: for=192.0.2.60;proto=http;by=203.0.113.43 Forwarded: for=192.0.2.43, for=198.51.100.17

From

The email address of the user making the request.
For example: From: user@example.com

Host

The domain name of the server, and the port numbers|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. If the request is generated directly in HTTP/2, it should not be used.
For example: Host: en.wikipedia.org:8080
Host: en.wikipedia.org

HTTP2-Settings

A request that upgrades from HTTP/1.1 to HTTP/2 MUST include exactly one HTTP2-Settings header field. The HTTP2-Settings header field is a connection-specific header field that includes parameters that govern the HTTP/2 connection, provided in anticipation of the server accepting the request to upgrade.
For example: HTTP2-Settings: token64

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.
For example: If-Match: "737060cd8c284d8af7ad3082f209582d"

If-Modified-Since

Allows a 304 Not Modified to be returned if content is unchanged.
For example: 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.
For example: If-None-Match: "737060cd8c284d8af7ad3082f209582d"

If-Range

If the entity is unchanged, send me the part that I am missing; otherwise, send me the entire new entity.
For example: If-Range: "737060cd8c284d8af7ad3082f209582d"

If-Unmodified-Since

Only send the response if the entity has not been modified since a specific time.
For example: 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.
For example: Max-Forwards: 10

Origin

Initiates a request for cross-origin resource sharing.
For example: Origin: http://www.example-social-network.com

Pragma

Implementation-specific fields that may have various effects anywhere along the request-response chain.
For example: Pragma: no-cache

Prefer

Allows client to request that certain behaviors be employed by a server while processing a request.
For example: Prefer: return=representation

Proxy-Authorization

Authorization credentials for connecting to a proxy.
For example: Proxy-Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ

Range

Request only part of an entity. Bytes are numbered from 0. See Byte serving.
For example: Range: bytes=500-999

Referer

The address of the previous web page from which a link to the currently requested page was followed.
Although the intended term is actually spelled "referrer", the misspelling is in the RFC as well as in most implementations, and is therefore considered correct terminology.
For example: 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 field Transfer-Encoding can be used, plus the "trailers" value to notify the server it expects to receive additional fields in the trailer after the last, zero-sized, chunk. Only trailers is supported in HTTP/2.
For example: TE: trailers, deflate

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.
For example: Trailer: Max-Forwards

Transfer-Encoding

The form of encoding used to safely transfer the entity to the user. are: chunked, compress, deflate, gzip, identity. Must not be used with HTTP/2.
For example: Transfer-Encoding: chunked

User-Agent

The user agent string of the user agent.
For example: User-Agent: Mozilla/5.0 Gecko/20100101 Firefox/12.0

Upgrade

Ask the server to upgrade to another protocol. Must not be used in HTTP/2.
For example: Upgrade: h2c, HTTPS/1.3, IRC/6.9, RTA/x11, websocket

Via

Informs the server of proxies through which the request was sent.
For example: Via: 1.0 fred, 1.1 example.com

Warning

A warning about a possible problem with the entity body. Since this header is often neither sent by servers nor acknowledged by clients, this header and its codes were obsoleted by the HTTP Working Group in 2022 with.
The following caching related warning codes were specified under RFC 7234.
; 110 Response is Stale
; 111 Revalidation Failed
; 112 Disconnected Operation
; 113 Heuristic Expiration
; 199 Miscellaneous Warning
; 214 Transformation Applied
; 299 Miscellaneous Persistent Warning
For example: Warning: 199 Miscellaneous warning

Common non-standard request fields

Upgrade-Insecure-Requests

Tells a server which hosts mixed content that the client would prefer redirection to HTTPS and can handle Content-Security-Policy: upgrade-insecure-requests
For example: Upgrade-Insecure-Requests: 1

X-Requested-With

Mainly used to identify Ajax requests ; this also identifies Android apps using WebView.
For example: X-Requested-With: XMLHttpRequest

DNT

Requests a web application to disable their tracking of a user. This is Mozilla's version of the X-Do-Not-Track header field. Safari and IE9 also have support for this field. On March 7, 2011, a draft proposal was submitted to IETF. The W3C Tracking Protection Working Group is producing a specification.
For example:
DNT: 1
DNT: 0

X-Forwarded-For

A de facto standard for identifying the originating IP address of a client connecting to a web server through an HTTP proxy or load balancer. Superseded by Forwarded header.
For example:
X-Forwarded-For: client1, proxy1, proxy2
X-Forwarded-For: 129.78.138.66, 129.78.64.103

X-Forwarded-Host

A de facto standard for identifying the original host requested by the client in the Host HTTP request header, since the host name and/or port of the reverse proxy may differ from the origin server handling the request. Superseded by Forwarded header.
For example:
X-Forwarded-Host: en.wikipedia.org:8080
X-Forwarded-Host: en.wikipedia.org

X-Forwarded-Proto

A de facto standard for identifying the originating protocol of an HTTP request, since a reverse proxy may communicate with a web server using HTTP even if the request to the reverse proxy is HTTPS. An alternative form of the header is used by Google clients talking to Google servers. Superseded by Forwarded header.
For example: X-Forwarded-Proto: https

Front-End-Https

Non-standard header field used by Microsoft applications and load-balancers.
For example: Front-End-Https: on

X-Http-Method-Override

Requests a web application to override the method specified in the request with the method given in the header field. This can be used when a user agent or firewall prevents PUT or DELETE methods from being sent directly.
For example: X-HTTP-Method-Override: DELETE

X-ATT-DeviceId

Allows easier parsing of the MakeModel/Firmware that is usually found in the User-Agent String of AT&T Devices.
For example: X-Att-Deviceid: GT-P7320/P7320XXLPG

X-Wap-Profile

Links to an XML file on the Internet with a full description and details about the device currently connecting. In the example to the right is an XML file for an AT&T Samsung Galaxy S2.
For example: x-wap-profile: http://wap.samsungmobile.com/uaprof/SGH-I777.xml

Proxy-Connection

Implemented as a misunderstanding of the HTTP specifications. Common because of mistakes in implementations of early HTTP versions. Has exactly the same functionality as standard Connection field. Must not be used with HTTP/2.
For example: Proxy-Connection: keep-alive

X-UIDH

Server-side deep packet inspection of a unique ID identifying customers of Verizon Wireless; also known as "perma-cookie" or "supercookie".
For example: X-UIDH:...

X-Csrf-Token

Used to prevent cross-site request forgery. Alternative header names are: X-CSRFToken and X-XSRF-TOKEN.
For example: X-Csrf-Token: i8XNjC4b8KVok4uw5RftR38Wgp2BFwql

X-Request-ID, X-Correlation-ID, Correlation-ID

Correlates HTTP requests between a client and server. Superseded by the traceparent header.
For example: X-Request-ID: f058ebd6-02f7-4d3f-942e-904344e8cde5

Save-Data

The Save-Data client hint request header available in Chrome, Opera, and Yandex browsers lets developers deliver lighter, faster applications to users who opt-in to data saving mode in their browser.
For example: Save-Data: on

Sec-GPC

The Sec-GPC request header indicates whether the user consents to a website or service selling or sharing their personal information with third parties.
For example: Sec-GPC: 1

Response fields

This section lists header fields used in a response.

Standard response fields

Accept-CH

Requests HTTP Client Hints.
For example: Accept-CH: UA, Platform

Access-Control-Allow-Origin, Access-Control-Allow-Credentials, Access-Control-Expose-Headers, Access-Control-Max-Age, Access-Control-Allow-Methods, Access-Control-Allow-Headers

Specifying which web sites can participate in cross-origin resource sharing.
For example: Access-Control-Allow-Origin: *

Accept-Patch

Specifies which patch document formats this server supports.
For example: Accept-Patch: text/example;charset=utf-8

Accept-Ranges

What partial content range types this server supports via byte serving.
For example: Accept-Ranges: bytes

Age

The age the object has been in a proxy cache in seconds.
For example: Age: 12

Allow

Valid methods for a specified resource. To be used for a 405 Method not allowed.
For example: Allow: GET, HEAD

Alt-Svc

A server uses "Alt-Svc" header to indicate that its resources can also be accessed at a different network location or using a different protocol. When using HTTP/2, servers should instead send an ALTSVC frame.
For example: Alt-Svc: http/1.1="http2.example.com:8001"; ma=7200

Cache-Control

Tells all caching mechanisms from server to client whether they may cache the response. A numeric value is in seconds.
If a web server responds with Cache-Control: no-cache, then a web browser or other caching system must not use the response to satisfy subsequent requests without first checking with the originating server. This header field is part of HTTP/1.1, and is ignored by some caches and browsers. It may be simulated by setting the Expires HTTP/1.0 header field value to a time earlier than the response time. Notice that is not instructing the browser or proxies about whether or not to cache the content. It tells the browser and proxies to validate the cache content with the server before using it. Sending a value thus instructs a browser or proxy to not use the cache contents merely based on "freshness criteria" of the cache content. Another common way to prevent old content from being shown to the user without validation is Cache-Control: max-age=0 which instructs the user agent that the content is stale and should be validated before use.
The value no-store instructs a browser to not cache the response, yet the browser is allowed to cache it none-the-less. In particular, the HTTP/1.1 definition draws a distinction between history stores and caches. If the user navigates back to a previous page, a browser may show a page that was stored on disk in the history store. This is correct behavior according to the specification. Many user agents provide different behavior in loading pages from the history store or cache depending on whether the protocol is HTTP or HTTPS.
For example: Cache-Control: max-age=3600

Connection

Control options for the current connection and list of hop-by-hop response fields. Must not be used with HTTP/2.
For example: Connection: close

Content-Disposition

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.
For example: Content-Disposition: attachment; filename="fname.ext"

Content-Encoding

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

Content-Language

The natural language or languages of the intended audience for the enclosed content.
For example: Content-Language: da

Content-Length

The length of the response body in octets.
For example: Content-Length: 348

Content-Location

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

Content-MD5

A Base64-encoded binary MD5 sum of the content of the response.
For example: Content-MD5: Q2hlY2sgSW50ZWdyaXR5IQ

Content-Range

Where in a full body message this partial message belongs.
For example: Content-Range: bytes 21010-47021/47022

Content-Type

The MIME type of this content.
For example: Content-Type: text/html; charset=utf-8

Date

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

Delta-Base

Specifies the delta-encoding entity tag of the response.
For example: Delta-Base: "abc"

ETag

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

Expires

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

IM

Instance-manipulations applied to the response.
For example: IM: feed

Last-Modified

The last modified date for the requested object.
For example: Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT

Link

Used to express a typed relationship with another resource, where the relation type is defined by RFC 8288.
For example: Link: </feed>; rel="alternate"

Location

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

P3P

This field 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 field with fake policy text, enough to fool browsers into thinking a P3P policy existed and granting permissions for third party cookies.
For example: P3P: CP="This is not a P3P policy! See https://en.wikipedia.org/wiki/Special:CentralAutoLogin/P3P for more info."

Pragma

Implementation-specific fields that may have various effects anywhere along the request-response chain.
For example: Pragma: no-cache

Preference-Applied

Indicates which Prefer tokens were honored by the server and applied to the processing of the request.
For example: Preference-Applied: return=representation

Proxy-Authenticate

Request authentication to access the proxy.
For example: Proxy-Authenticate: Basic

Public-Key-Pins

HTTP Public Key Pinning, announces hash of website's authentic TLS certificate.
For example: Public-Key-Pins: max-age=2592000; pin-sha256="E9CZ9INDbd+2eRQozYqqbQ2yXLVKB9+xcprMF+44U1g=";

Retry-After

If an entity is temporarily unavailable, this instructs the client to try again later. Value could be a specified period of time or a HTTP-date.
For example 1: Retry-After: 120
For example 2: Retry-After: Fri, 07 Nov 2014 23:59:59 GMT

Server

A name for the server.
For example: Server: Apache/2.4.1

Set-Cookie

An HTTP cookie.
For example: Set-Cookie: CookieName=CookieValue; Max-Age=3600; Version=1

Strict-Transport-Security

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

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.
For example: Trailer: Max-Forwards

Transfer-Encoding

The form of encoding used to safely transfer the entity to the user. are: chunked, compress, deflate, gzip, identity. Must not be used with HTTP/2.
For example: Transfer-Encoding: chunked

Tk

Tracking Status header, value suggested to be sent in response to a DNT request. Possible values:

"!" — under construction
"?" — dynamic
"G" — gateway to multiple parties
"N" — not tracking
"T" — tracking
"C" — tracking with consent
"P" — tracking only if consented
"D" — disregarding DNT
"U" — updated

For example: Tk: ?

Upgrade

Ask the client to upgrade to another protocol. Must not be used in HTTP/2.
For example: Upgrade: h2c, HTTPS/1.3, IRC/6.9, RTA/x11, websocket

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.
For example 1: Vary: *
For example 2: Vary: Accept-Language

Via

Informs the client of proxies through which the response was sent.
For example: Via: 1.0 fred, 1.1 example.com

Warning

A general warning about possible problems with the entity body.
For example: Warning: 199 Miscellaneous warning

WWW-Authenticate

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

X-Frame-Options

Clickjacking protection: deny - no rendering within a frame, sameorigin - no rendering if origin mismatch, allow-from - allow from specified location, allowall - non-standard, allow from any location.
For example: X-Frame-Options: deny

Common non-standard response fields

Content-Security-Policy, X-Content-Security-Policy, X-WebKit-CSP

Content Security Policy definition.
For example:
X-WebKit-CSP: default-src 'self'

Expect-CT

Notify to prefer to enforce Certificate Transparency.
For example:
Expect-CT: max-age=604800, enforce, report-uri="https://example.example/report"

NEL

Used to configure network request logging.
For example:

Permissions-Policy

To allow or disable different features or APIs of the browser.
For example:
Permissions-Policy: fullscreen=, camera=, microphone=, geolocation=, interest-cohort=

Refresh

Tells the browser to refresh the page or redirect to a different URL, either after a given number of seconds, Introduced by Netscape in 1995 and has since become a de facto standard supported by most web browsers. Was eventually standardized in the HTML Living Standard in 2017.
For example:
Refresh: 5; url=http://www.w3.org/pub/WWW/People.html

Report-To

Instructs the user agent to store reporting endpoints for an origin.
For example:

Status

CGI header field specifying the status of the HTTP response. Normal HTTP responses use a separate "Status-Line" instead, defined by RFC 9110.
For example:
Status: 200 OK

Timing-Allow-Origin

The Timing-Allow-Origin response header specifies origins that are allowed to see values of attributes retrieved via features of the, which would otherwise be reported as zero due to cross-origin restrictions.
For example:
Timing-Allow-Origin: *
Timing-Allow-Origin: <origin>*

X-Content-Duration

Provide the duration of the audio or video in seconds. Not supported by current browsers – the header was only supported by Gecko browsers, from which support was removed in 2015.
For example:
X-Content-Duration: 42.666

X-Content-Type-Options

The only defined value, "nosniff", prevents Internet Explorer from MIME-sniffing a response away from the declared content-type. This also applies to Google Chrome, when downloading extensions.
For example:
X-Content-Type-Options: nosniff

X-Powered-By

Specifies the technology supporting the web application.
For example:
X-Powered-By: PHP/5.4.0

X-Redirect-By

Specifies the component that is responsible for a particular redirect.
For example:
X-Redirect-By: WordPress
X-Redirect-By: Polylang

X-Request-ID, X-Correlation-ID

Correlates HTTP requests between a client and server.
For example:
X-Request-ID: f058ebd6-02f7-4d3f-942e-904344e8cde5

X-UA-Compatible

Recommends the preferred rendering engine to use to display the content. Also used to activate Chrome Frame in Internet Explorer. In HTML Standard, only the IE=edge value is defined.
For example:
X-UA-Compatible: IE=edge
X-UA-Compatible: IE=EmulateIE7
X-UA-Compatible: Chrome=1

X-XSS-Protection

Cross-site scripting filter
For example:
X-XSS-Protection: 1; mode=block