Page Speed Hints

      High This Hint is very important, and definitely warrants attention. Issue This Hint represents an error or problem that needs to be fixed.

      Static resources have private cache-control header

      This means that the URL in question is a resource URL, such as images or JavaScript files, which specifies a private cache-control header.

      Why is this important?

      Private cache-control headers are typically intended for customizing the browsing experience for a single user (e.g. a logged in user), whereby the resources are only cached privately - within the end-user's local browser cache.

      When the cache-control header is set to private, this means that the resource can only be cached locally, and not on a shared cache. A shared cache is a cache that stores responses to be reused by more than one user. For example, an ISP or your company might have set up a web proxy as part of its local network infrastructure to serve many users so that popular resources are reused a number of times, reducing network traffic and latency.

      What does the Hint check?

      This Hint will trigger for any internal resource URL that sets the cache-control header to private.

      Examples that trigger this Hint:

      Resource file URLs that set a private cache-control header:

      HTTP/... 200 OK

      ...
      Cache-Control => private
      Content-Type => image/png

      How do you resolve this issue?

      Static content should available to all users, and presents an opportunity for aggressive caching, so setting the cache-control to private is wasteful. Once you have checked the resource files in question, and determined that they do not require a private cache-control header, replace 'private' with 'max-age=<seconds>', allowing as much time as possible for each resource.

      Follow the decision tree below to determine the optimal caching policy for a particular resource, or a set of resources, that your application uses.

      Defining cache decisions

      Further Reading

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