Abstract: A web content builder tool is provided for rapidly creating multiple related web content layouts for dynamic serving to devices having, e.g., different form factors. Layouts can be selectably linked or unlinked. While linked, adding content items to one layout causes automatic propagation of family member content items to the other layouts, and changing content item attributes within one layout causes automatic propagation of changes to family member content items in other layouts. While unlinked, adding or changing content items in one layout does not automatically cause changes to other layouts.