Hello DP mates. As you guys know, Page Speed is one big factor of SEO today. All tests that I've been doing (GTMetrix, Pingdom Tools...) always suggest this for me: Specify a cache validator The following resources are missing a cache validator. Resources that do not specify a cache validator cannot be refreshed efficiently. Specify a Last-Modified or ETag header to enable cache validation for the following resources: (lists lots of .jpg, .png, .js and .css files) And suggest the reading of this page: https://developers.google.com/speed/docs/best-practices/caching?hl=sv#LeverageBrowserCaching I've searched the whole net for it, and I wasn't able to understand what the damn hell I should do to fix this problem. Can someone help me?