Avoid Private Headers on Static Content

For more information about the importance of Cache-Control Headers, see the article on Avoiding Extra Requests with Cache-Control Headers.

Static content refers to the kind of data that makes up a web page that does not usually change very frequently. Static content is any content that can be delivered to an end user without having to be generated, modified, or processed. It is usually composed of items such as CSS, Javascript and image files.  

Many Internet Service Providers and network operators provide caching services on their networks to help speed up the websites their users visit. Instead of loading all of the data for a cached website for each user, the network caching service will use as much cached data as possible to load the website for every user who visits the website. The purpose of private cache headers is to inform these services to not save copies of the data that their visitors download from the Internet, to ensure they receive the correct information from the website itself rather than the cached version.Since it is not updated frequently, static content should be cached by these network caching services. Private cache headers should not be set on static content like JavaScript, CSS, or images so that these files can be cached to speed up how quickly your website loads for all of the users of an Internet Service Provider or network operator.