Cache-Control

The Cache-Control general-header field is used to specify directives for caching mechanisms in both, requests and responses. Caching directives are unidirectional, meaning that a given directive in a request is not implying that the same directive is to be given in the response.

Header type General header
Forbidden header name no

Syntax

The directives are case-insensitive and have an optional argument, that can use both token and quoted-string syntax. Multiple directives are comma-separated.

Cache request directives

Standard Cache-Control directives that can be used by the client in an HTTP request.

Cache-Control: max-age=<seconds>
Cache-Control: max-stale[=<seconds>]
Cache-Control: min-fresh=<seconds>
Cache-control: no-cache 
Cache-control: no-store
Cache-control: no-transform
Cache-control: only-if-cached

Cache response directives

Standard Cache-Control directives that can be used by the server in an HTTP response.

Cache-control: must-revalidate
Cache-control: no-cache
Cache-control: no-store
Cache-control: no-transform
Cache-control: public
Cache-control: private
Cache-control: proxy-revalidate
Cache-Control: max-age=<seconds>
Cache-control: s-maxage=<seconds>

Extension Cache-Control directives

Extension Cache-Control directives are not part of the core HTTP caching standards document. Be sure to check the compatibility table for their support.

Cache-control: immutable 
Cache-control: stale-while-revalidate=<seconds>
Cache-control: stale-if-error=<seconds>

Directives

Cacheability

public
Indicates that the response may be cached by any cache.
private
Indicates that the response is intended for a single user and must not be stored by a shared cache. A private cache may store the response.
no-cache
Forces caches to submit the request to the origin server for validation before releasing a cached copy.
only-if-cached
Indicates to not retrieve new data. The client only wishes to obtain a cached response, and should not contact the origin-server to see if a newer copy exists.

Expiration

max-age=<seconds>
Specifies the maximum amount of time a resource will be considered fresh. Contrary to Expires, this directive is relative to the time of the request.
s-maxage=<seconds>
Overrides max-age or the Expires header, but it only applies to shared caches (e.g., proxies) and is ignored by a private cache.
max-stale[=<seconds>]
Indicates that the client is willing to accept a response that has exceeded its expiration time. Optionally, you can assign a value in seconds, indicating the time the response must not be expired by.
min-fresh=<seconds>
Indicates that the client client wants a response that will still be fresh for at least the specified number of seconds.
stale-while-revalidate=<seconds>
...
stale-if-error=<seconds>
...

Revalidation and reloading

must-revalidate
The cache must verify the status of the stale resources before using it and expired ones should not be used.
proxy-revalidate
Same as must-revalidate, but it only applies to shared caches (e.g., proxies) and is ignored by a private cache.
immutable
Indicates that the response body will not change over time. The resource, if unexpired, is unchanged on the server and therefore the client should not send a conditional revalidation for it (e.g. If-None-Match or If-Modified-Since) to check for updates. Clients that aren't aware of this extension must ignore them as per the HTTP specification. In Firefox, immutable is only honored on https:// transactions. For more information, see also this blog post.

Other

no-store
The cache should not store anything about the client request or server response.
no-transform
No transformations or conversions should made to the resource. The Content-Encoding, Content-Range, Content-Type headers must not be modified by a proxy. A non- transparent proxy might, for example, convert between image formats in order to save cache space or to reduce the amount of traffic on a slow link. The no-transform directive disallows this.

Examples

Preventing caching

To turn off caching, you can send the following directives. In addition, see also the Expires and Pragma headers.

Cache-Control: no-cache, no-store, must-revalidate

Caching static assets

For the files in the application that will not change, you can usually add aggressive caching. This includes static files that are served by the application such as images, CSS files and JavaScript files, for example. In addition, see also the Expires header.

Cache-Control:public, max-age=31536000

Specifications

Specification Title
RFC 7234 Hypertext Transfer Protocol (HTTP/1.1): Caching
RFC 5861 HTTP Cache-Control Extensions for Stale Content

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari Servo
Basic Support(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)(Yes)
immutableNo supportNo support49.0No supportNo supportNo support?
stale-while-revalidateNo support1No supportNo support2No supportNo supportNo supportNo support
stale-if-errorNo support1No supportNo support2No supportNo supportNo supportNo 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)
immutableNo supportNo supportNo supportNo supportNo supportNo supportNo support
stale-while-revalidateNo supportNo supportNo supportNo supportNo supportNo supportNo support
stale-if-errorNo supportNo supportNo supportNo supportNo supportNo supportNo support

1. See Chromium bug 348877.

2. See Bugzilla bug 995651.

See also

Document Tags and Contributors

 Contributors to this page: fscholz, Life777
 Last updated by: fscholz,