Baseline Widely available *
The HTTP Set-Cookie response header is used to send a cookie from the server to the user agent, so that the user agent can send it back to the server later. To send multiple cookies, multiple Set-Cookie headers should be sent in the same response.
For more information, see the guide on Using HTTP cookies.
SyntaxSet-Cookie: <cookie-name>=<cookie-value>
Set-Cookie: <cookie-name>=<cookie-value>; Domain=<domain-value>
Set-Cookie: <cookie-name>=<cookie-value>; Expires=<date>
Set-Cookie: <cookie-name>=<cookie-value>; HttpOnly
Set-Cookie: <cookie-name>=<cookie-value>; Max-Age=<number>
Set-Cookie: <cookie-name>=<cookie-value>; Partitioned
Set-Cookie: <cookie-name>=<cookie-value>; Path=<path-value>
Set-Cookie: <cookie-name>=<cookie-value>; Secure
Set-Cookie: <cookie-name>=<cookie-value>; SameSite=Strict
Set-Cookie: <cookie-name>=<cookie-value>; SameSite=Lax
Set-Cookie: <cookie-name>=<cookie-value>; SameSite=None; Secure
// Multiple attributes are also possible, for example:
Set-Cookie: <cookie-name>=<cookie-value>; Domain=<domain-value>; Secure; HttpOnly
<cookie-name>=<cookie-value>
Defines the cookie name and its value. A cookie definition begins with a name-value pair.
A <cookie-name> can contain any US-ASCII characters except for: control characters (ASCII characters 0 up to 31 and ASCII character 127) or separator characters (space, tab and the characters: ( ) < > @ , ; : \ " / [ ] ? = { })
A <cookie-value> can optionally be wrapped in double quotes and include any US-ASCII character excluding control characters (ASCII characters 0 up to 31 and ASCII character 127), Whitespace, double quotes, commas, semicolons, and backslashes.
Encoding: Many implementations perform percent-encoding on cookie values. However, this is not required by the RFC specification. The percent-encoding does help to satisfy the requirements of the characters allowed for <cookie-value>.
Note: Some <cookie-name> have a specific semantic:
__Secure- prefix: Cookies with names starting with __Secure- (dash is part of the prefix) must be set with the secure flag from a secure page (HTTPS).
__Host- prefix: Cookies with names starting with __Host- are sent only to the host subdomain or domain that set them, and not to any other host. They must be set with the secure flag, must be from a secure page (HTTPS), must not have a domain specified, and the path must be /.
Domain=<domain-value> Optional
Defines the host to which the cookie will be sent.
Only the current domain can be set as the value, or a domain of a higher order, unless it is a public suffix. Setting the domain will make the cookie available to it, as well as to all its subdomains.
If omitted, this attribute defaults to the host of the current document URL, not including subdomains.
Contrary to earlier specifications, leading dots in domain names (.example.com) are ignored.
Multiple host/domain values are not allowed, but if a domain is specified, then subdomains are always included.
Expires=<date> Optional
Indicates the maximum lifetime of the cookie as an HTTP-date timestamp. See Date for the required formatting.
If unspecified, the cookie becomes a session cookie. A session finishes when the client shuts down, after which the session cookie is removed.
Warning: Many web browsers have a session restore feature that will save all tabs and restore them the next time the browser is used. Session cookies will also be restored, as if the browser was never closed.
The Expires attribute is set by the server with a value relative to its own internal clock, which may differ from that of the client browser. Firefox and Chromium-based browsers internally use an expiry (max-age) value that is adjusted to compensate for clock difference, storing and expiring cookies based on the time intended by the server. The adjustment for clock skew is calculated from the value of the DATE header. Note that the specification explains how the attribute should be parsed, but does not indicate if/how the value should be corrected by the recipient.
HttpOnly Optional
Forbids JavaScript from accessing the cookie, for example, through the Document.cookie property. Note that a cookie that has been created with HttpOnly will still be sent with JavaScript-initiated requests, for example, when calling XMLHttpRequest.send() or fetch(). This mitigates attacks against cross-site scripting (XSS).
Max-Age=<number> Optional
Indicates the number of seconds until the cookie expires. A zero or negative number will expire the cookie immediately. If both Expires and Max-Age are set, Max-Age has precedence.
Partitioned Optional
Indicates that the cookie should be stored using partitioned storage. Note that if this is set, the Secure directive must also be set. See Cookies Having Independent Partitioned State (CHIPS) for more details.
Path=<path-value> Optional
Indicates the path that must exist in the requested URL for the browser to send the Cookie header.
The forward slash (/) character is interpreted as a directory separator, and subdirectories are matched as well. For example, for Path=/docs,
/docs, /docs/, /docs/Web/, and /docs/Web/HTTP will all match./, /docsets, /fr/docs will not match.Note: The path attribute lets you control what cookies the browser sends based on the different parts of a site. It is not intended as a security measure, and does not protect against unauthorized reading of the cookie from a different path.
SameSite=<samesite-value> Optional
Controls whether or not a cookie is sent with cross-site requests: that is, requests originating from a different site, including the scheme, from the site that set the cookie. This provides some protection against certain cross-site attacks, including cross-site request forgery (CSRF) attacks.
The possible attribute values are:
Strict
Send the cookie only for requests originating from the same site that set the cookie.
Lax
Send the cookie only for requests originating from the same site that set the cookie, and for cross-site requests that meet both of the following criteria:
The request is a top-level navigation: this essentially means that the request causes the URL shown in the browser's address bar to change.
This would exclude, for example, requests made using the fetch() API, or requests for subresources from <img> or <script> elements, or navigations inside <iframe> elements.
It would include requests made when the user clicks a link in the top-level browsing context from one site to another, or an assignment to document.location, or a <form> submission.
The request uses a safe method: in particular, this excludes POST, PUT, and DELETE.
Some browsers use Lax as the default value if SameSite is not specified: see Browser compatibility for details.
Note: When Lax is applied as a default, a more permissive version is used. In this more permissive version, cookies are also included in POST requests, as long as they were set no more than two minutes before the request was made.
None
Send the cookie with both cross-site and same-site requests. The Secure attribute must also be set when using this value.
Secure Optional
Indicates that the cookie is sent to the server only when a request is made with the https: scheme (except on localhost), and therefore, is more resistant to man-in-the-middle attacks.
Note: Do not assume that Secure prevents all access to sensitive information in cookies (session keys, login details, etc.). Cookies with this attribute can still be read/modified either with access to the client's hard disk or from JavaScript if the HttpOnly cookie attribute is not set.
Insecure sites (http:) cannot set cookies with the Secure attribute. The https: requirements are ignored when the Secure attribute is set by localhost.
Session cookies are removed when the client shuts down. Cookies are session cookies if they do not specify the Expires or Max-Age attribute.
Set-Cookie: sessionId=38afes7a8
Permanent cookies are removed at a specific date (Expires) or after a specific length of time (Max-Age) and not when the client is closed.
Set-Cookie: id=a3fWa; Expires=Wed, 21 Oct 2015 07:28:00 GMT
Set-Cookie: id=a3fWa; Max-Age=2592000
A cookie for a domain that does not include the server that set it should be rejected by the user agent.
The following cookie will be rejected if set by a server hosted on original-company.com:
Set-Cookie: qwerty=219ffwef9w0f; Domain=some-company.co.uk
A cookie for a subdomain of the serving domain will be rejected.
The following cookie will be rejected if set by a server hosted on example.com:
Set-Cookie: sessionId=e8bb43229de9; Domain=foo.example.com
Cookie names prefixed with __Secure- or __Host- can be used only if they are set with the secure attribute from a secure (HTTPS) origin.
In addition, cookies with the __Host- prefix must have a path of / (meaning any path at the host) and must not have a Domain attribute.
Warning: For clients that don't implement cookie prefixes, you cannot count on these additional assurances, and prefixed 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 attribute
Set-Cookie: __Secure-id=1
// Rejected due to the missing Path=/ attribute
Set-Cookie: __Host-id=1; Secure
// Rejected due to setting a Domain
Set-Cookie: __Host-id=1; Secure; Path=/; Domain=example.com
Set-Cookie: __Host-example=34d8g; SameSite=None; Secure; Path=/; Partitioned;
Note: Partitioned cookies must be set with Secure. In addition, it is recommended to use the __Host prefix when setting partitioned cookies to make them bound to the hostname and not the registrable domain.
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