1. A computer implemented method comprising: receiving, at a server computer, a first request from a client computer for a first content item of a web page, the first request received in response to a user request for the web page at the client computer; interpreting, based on the first request being an initial request for content of the web page, that the first request is for one or more default content items of the web page; identifying one or more default content items of the web page based on the one or more default content items being pre-classified as default content items; responding to the first request with the one or more default content items of the web page for display as part of the web page and without providing one or more non-default content items of the web page with the one or more default content items; receiving, at a server computer, a second request from the client computer for a second content item of the web page, the second request being interpreted to be a request for the one or more non-default content items of the web page and being received in response to a user interaction with the one or more default content items of the web page; identifying one or more non-default content items of the web page based on the one or more non-default content items being pre-classified as non-default content items; and responding to the second request with the one or more non-default content items of the web page for display as part of the web page.