The HTTP Response Headers List

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A reference to the HTTP response headers, from Cache-Control, Content-Type, ETag and Location to Set-Cookie, Strict-Transport-Security and the CORS headers.

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Every HTTP response can have a set of headers.

This post aims to list all those headers, and describe them.

Standard headers

Accept-Patch

Accept-Patch: text/example;charset=utf-8

Specifies which patch document formats this server supports

Accept-Ranges

Accept-Ranges: bytes

What partial content range types this server supports via byte serving

Age

Age: 12

The age the object has been in a proxy cache in seconds

Allow

Allow: GET, HEAD

Valid methods for a specified resource. To be used for a 405 Method not allowed

Alt-Svc

Alt-Svc: http/1.1= "http2.example.com:8001"; ma=7200

A server uses “Alt-Svc” header (meaning Alternative Services) to indicate that its resources can also be accessed at a different network location (host or port) or using a different protocol. When using HTTP/2, servers should instead send an ALTSVC frame

Cache-Control

Cache-Control: max-age=3600 Cache-Control: no-cache, no-store, max-age=0, must-revalidate

If no-cache is used, the Cache-Control header can tell the browser to never use a cached version of a resource without first checking the ETag value.

max-age is measured in seconds

The more restrictive no-store option tells the browser (and all the intermediary network devices) the not even store the resource in its cache:

Cache-Control: no-store

Connection

Connection: close

Control options for the current connection and list of hop-by-hop response fields. Deprecated in HTTP/2

Content-Disposition

Content-Disposition: attachment; filename="file.txt"

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

Content-Encoding

Content-Encoding: gzip

The type of encoding used on the data. See HTTP compression

Content-Language

Content-Language: en

The natural language or languages of the intended audience for the enclosed content

Content-Length

Content-Length: 348

The length of the response body expressed in 8-bit bytes

Content-Location

Content-Location: /index.htm

An alternate location for the returned data

Content-Range

Content-Range: bytes 21010-47021/47022

Where in a full body message this partial message belongs

Content-Type

Content-Type: text/html; charset=utf-8

The MIME type of this content

Date

Date: Tue, 15 Nov 1994 08:12:31 GMT

The date and time that the message was sent (in “HTTP-date” format as defined by RFC 7231)

Delta-Base

Delta-Base: "abc"

Specifies the delta-encoding entity tag of the response

ETag

ETag: "737060cd8c284d8a[...]"

An identifier for a specific version of a resource, often a message digest

Expires

Expires: Sat, 01 Dec 2018 16:00:00 GMT

Gives the date/time after which the response is considered stale (in “HTTP-date” format as defined by RFC 7231)

IM

IM: feed

Instance-manipulations applied to the response

Last-Modified

Last-Modified: Mon, 15 Nov 2017 12:00:00 GMT

The last modified date for the requested object (in “HTTP-date” format as defined by RFC 7231)

Link: </feed>; rel="alternate"

Used to express a typed relationship with another resource, where the relation type is defined by RFC 5988

Location

Location: /pub/WWW/People.html

Used in redirection, or when a new resource has been created

Permissions-Policy

Permissions-Policy: geolocation=(), microphone=()

Lets the site allow or block browser features (camera, microphone, geolocation and more) for its own pages and for the iframes it embeds. It replaced the Feature-Policy header. As of September 2026 only Chromium-based browsers read the header. Firefox and Safari support the allow attribute on iframe, but not the header

Pragma

Pragma: no-cache

Implementation-specific fields that may have various effects anywhere along the request-response chain.

Proxy-Authenticate

Proxy-Authenticate: Basic

Request authentication to access the proxy

Public-Key-Pins

Obsolete. HTTP Public Key Pinning (HPKP) announced the hashes of the site’s TLS keys, so the browser could refuse a different certificate later. Chrome removed it in version 72 and Firefox in version 72, and no browser reads it today. Certificate Transparency took its place, and browsers enforce that without any response header

Retry-After

Retry-After: 120 Retry-After: Fri, 07 Nov 2014 23:59:59 GMT

If an entity is temporarily unavailable, this instructs the client to try again later. Value could be a specified period of time (in seconds) or a HTTP-date

Server

Server: Apache/2.4.1 (Unix)

A name for the server

Set-Cookie: UserID=JohnDoe; Max-Age=3600; Version=1

An HTTP cookie

Strict-Transport-Security

Strict-Transport-Security: max-age=16070400; includeSubDomains

A HSTS Policy informing the HTTP client how long to cache the HTTPS only policy and whether this applies to subdomains

Trailer

Trailer: Max-Forwards

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

Transfer-Encoding

Transfer-Encoding: chunked

The form of encoding used to safely transfer the entity to the user. Currently defined methods are: chunked, compress, deflate, gzip, identity. Deprecated in HTTP/2

Tk

Obsolete. The Tracking Status header was the server’s answer to the DNT (Do Not Track) request header. DNT was abandoned: Safari dropped it in version 12.1 and Firefox in version 135. The privacy signal browsers send today is Global Privacy Control, the Sec-GPC request header

Upgrade

Upgrade: h2c, HTTPS/1.3, IRC/6.9, RTA/x11, websocket

Ask the client to upgrade to another protocol. Deprecated in HTTP/2

Vary

Vary: Accept-Language 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

Via

Via: 1.0 fred, 1.1 example.com (Apache/1.1)

Informs the client of proxies through which the response was sent

Warning

Obsolete since RFC 9111 (2022). It carried a general warning about the entity body, for example that it came from a stale cache. Clients ignore it now, and Age plus the Cache-Status header (RFC 9211) cover the caching cases it was used for

WWW-Authenticate

WWW-Authenticate: Basic

Indicates the authentication scheme that should be used to access the requested entity

CORS headers

Non-standard headers:

Content-Security-Policy

Helps to protect against XSS attacks. See MDN for more details

Writing this header by hand is error-prone, so I built a free CSP generator that puts together a valid Content-Security-Policy for you.

Read Content Security Policy explained for directives, nonces, hashes, and report-only rollout.

Refresh

Refresh: 10;http://www.example.org/

Redirect to a URL after an arbitrary delay expressed in seconds

X-Powered-By

X-Powered-By: Brain/0.6b

Can be used by servers to send their name and version

X-Request-ID

Allows the server to pass a request ID that clients can send back to let the server correlate the request

X-UA-Compatible

X-UA-Compatible: IE=Edge

Legacy. Picked the document mode of Internet Explorer 8 to 11 (IE=Edge meant the newest one). No current browser reads it. See What is the Doctype for the meta tag version of the same thing

X-XSS-Protection

Now replaced by the Content-Security-Policy header, used in older browsers to stop pages load when an XSS attack is detected

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