{"id":112,"date":"2017-08-13T14:38:29","date_gmt":"2017-08-13T14:38:29","guid":{"rendered":"https:\/\/www.imperva.com\/learn\/?post_type=performance&p=112"},"modified":"2024-05-22T12:13:02","modified_gmt":"2024-05-22T12:13:02","slug":"cache-control","status":"publish","type":"performance","link":"https:\/\/www.imperva.com\/learn\/performance\/cache-control\/","title":{"rendered":"Cache Control"},"content":{"rendered":"

What is the Cache-Control Header<\/h2>\n

Cache-control is an HTTP header used to specify\u00a0browser caching<\/a>\u00a0policies in both client requests and server responses. Policies include how a resource is cached, where it\u2019s cached and its maximum age before expiring (i.e.,\u00a0time to live<\/a>).<\/p>\n

The cache-control header is broken up into directives, the most common of which are detailed below:<\/p>\n

\"An

An example of an HTTP Response Header from google.com<\/p><\/div>\n

Cache-Control: Max-Age<\/h2>\n

The max-age request directive defines, in seconds, the amount of time it takes for a cached copy of a resource to expire. After expiring, a browser must refresh its version of the resource by sending another request to a server.<\/p>\n

For example,\u00a0cache-control: max-age=120<\/code>\u00a0means that the returned resource is valid for 120 seconds, after which the browser has to request a newer version.<\/p>\n

Cache-Control: No-Cache<\/h2>\n

The no-cache directive means that a browser may cache a response, but must first submit a validation request to an\u00a0origin server<\/a>.<\/p>\n

Cache-Control: No-Store<\/h2>\n

The no-store directive means browsers aren\u2019t allowed to cache a response and must pull it from the server each time it\u2019s requested. This setting is usually used for sensitive data, such as personal banking details.<\/p>\n

Cache-Control: Public<\/h2>\n

The public response directive indicates that a resource can be cached by any cache.<\/p>\n

Cache-Control: Private<\/h2>\n

The private response directive indicates that a resource is user specific\u2014it can still be cached, but only on a client device. For example, a web page response marked as private can be cached by a desktop browser, but not a content delivery network (CDN).<\/p>\n

Additional HTTP Cache Headers<\/h2>\n

In addition to cache-control, notable HTTP cache headers include:<\/p>\n