Set-Cookie

The Set-Cookie HTTP response header is used to send cookies from the server to the user agent.

For more information, see the guide on HTTP cookies.

Header type Response header
Forbidden header name no

Syntax

Set-Cookie: <cookie-name>=<cookie-value> 
Set-Cookie: <cookie-name>=<cookie-value>; Expires=<date>
Set-Cookie: <cookie-name>=<cookie-value>; Max-Age=<non-zero-digit>
Set-Cookie: <cookie-name>=<cookie-value>; Domain=<domain-value>
Set-Cookie: <cookie-name>=<cookie-value>; Path=<path-value>
Set-Cookie: <cookie-name>=<cookie-value>; Secure
Set-Cookie: <cookie-name>=<cookie-value>; HttpOnly

Set-Cookie: <cookie-name>=<cookie-value>; SameSite=Strict
Set-Cookie: <cookie-name>=<cookie-value>; SameSite=Lax

// Multiple directives are also possible, for example:
Set-Cookie: <cookie-name>=<cookie-value>; Domain=<domain-value>; Secure; HttpOnly

Directives

<cookie-name>=<cookie-value>
A cookie begins with a name-value pair:
  • A <cookie-name> can be anything but control characters (CTLs) or spaces and tabs. It also must not contain a separator character like the following: ( ) < > @ , ; : \ " /  [ ] ? = { }.
  • A <cookie-value> can optionally be set in double quotes and any US-ASCII characters excluding CTLs, whitespace, double quotes, comma, semicolon, and backslash are allowed. Encoding: Many implementations perform URL encoding on cookie values, however it is not required per the RFC specification. It does help satisfying the requirements about which characters are allowed for <cookie-value> though.
  • __Secure- prefix: Cookies with a name starting with __Secure- (dash is part of the prefix) must be set with the secure flag and must be from a secure page (HTTPS).
  • __Host- prefix: Cookies with a name starting with __Host- must be set with the secure flag, must be from a secure page (HTTPS), must not have a domain specified (and therefore aren't send to subdomains) and the path must be "/".
Expires=<date> Optional

The maximum lifetime of the cookie as an HTTP-date timestamp. See Date for the detailed format. If not specified, the cookie will have the lifetime of a session cookie. A session is finished when the client is shut down meaning that session cookies will get removed at that point. However, many web browsers have a feature called session restore that will save all your tabs and have them come back next time you use the browser. Cookies will also be present and it's like you had never actually closed the browser.

Max-Age=<non-zero-digit> Optional
Number of seconds until the cookie expires. One or more digits 1 through 9. Older browsers (ie6, ie7, and ie8) do not support max-age. For other browsers, if both (Expires and Max-Age) are set, Expires will have precedence.
Domain=<domain-value> Optional
Specifies those hosts to which the cookie will be sent. If not specified, defaults to the host portion of the current document location (but not including subdomains). Contrary to earlier specifications, leading dots in domain names are ignored. If a domain is specified, subdomains are always included.
Path=<path-value> Optional
Indicates a URL path that must exist in the requested resource before sending the Cookie header. The %x2F ("/") character is interpreted as a directory separator and sub directories will be matched as well (e.g. path=/docs, "/docs", "/docs/Web/", or "/docs/Web/HTTP" will all be matched).
Secure Optional
A secure cookie will only be sent to the server when a request is made using SSL and the HTTPS protocol.

Confidential or sensitive information should never be stored or transmitted in HTTP Cookies as the entire mechanism is inherently insecure.

HttpOnly Optional
HTTP-only cookies aren't accessible via JavaScript through the Document.cookie property, the XMLHttpRequest and Request APIs to prevent attacks against cross-site scripting (XSS).
SameSite=Strict
SameSite=Lax Optional 

Allows servers to assert that a cookie ought not to be sent along with cross-site requests, which provides some protection against cross-site request forgery attacks (CSRF).

Examples

Session cookies will get removed when the client is shut down. They don's specify the Expires or Max-Age directives. Note that web browser have often enabled session restoring.

Set-Cookie: sessionid=38afes7a8; httponly; Path=/

Instead of expiring when the client is closed, permanent cookies expire at a specific date (Expires) or after a specific length of time (Max-Age).

Set-Cookie: id=a3fWa; Expires=Wed, 21 Oct 2015 07:28:00 GMT; Secure; HttpOnly

A third-party cookie belongs to a domain different from the one currently shown in the address bar. These cookies are usually set by advertisements and open up the potential for tracking the user's browsing history.

Set-Cookie: qwerty=219ffwef9w0f; Domain=somecompany.co.uk; Path=/; Expires=Wed, 30 Aug 2019 00:00:00 GMT

For clients that implement the additional assurances as specified with the special naming prefix, the cookies will only be accepted if set from a secure origin (HTTPS) and if they have the required flags set. For clients that don't implement cookie prefixes, you cannot count on having these additional assurances and the cookies will always be accepted.

// Both accepted when from a secure origin (HTTPS)
Set-Cookie: __Secure-ID=123; Secure; Domain=example.com
Set-Cookie: __Host-ID=123; Secure; Path=/

// Rejected due to missing Secure directive
Set-Cookie: __Secure-id=1

// Rejected due to the missing Secure and Path=/ directives
Set-Cookie: __Host-id=1

// Rejected due to the missing Path=/ directive
Set-Cookie: __Host-id=1; Secure'; 

Specifications

Specification Title
RFC 6265, section 4.1: Set-Cookie HTTP State Management Mechanism
RFC draft-ietf-httpbis-cookie-prefixes-00 Cookie Prefixes
RFC draft-ietf-httpbis-cookie-same-site-00 Same-Site Cookies

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari Servo
Basic Support(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)?
Max-Age(Yes)(Yes)(Yes)8.0(Yes)(Yes)?
HttpOnly1.0(Yes)3.09.0115.0?
Cookie prefixes49(Yes)50?36(Yes)?
SameSite51No supportNo support1No support39No support?
Feature Android Chrome for Android Edge Mobile Firefox for Android IE Mobile Opera Mobile Safari Mobile
Basic Support(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)
Max-Age(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)
HttpOnly?(Yes)(Yes)1.0(Yes)(Yes)iOS 4
Cookie prefixes?49(Yes)50?36(Yes)
SameSite5151No supportNo support1No support39No support

1. See Bugzilla bug 795346.

See also

Document Tags and Contributors

 Contributors to this page: fscholz, teoli
 Last updated by: fscholz,