Systems and methods for automatically identifying visually sensible locations in which third-party content can be placed on a web page and configuring the web page to display third-party content at the identified locations. A processor identifies a root element of a web page within which to insert third-party content slots for providing third-party content items. The processor identifies visible content items within the root element and identifies anchorable elements within the root element around which a third-party content slot is insertable. Each of the anchorable elements corresponds to a respective identified visible content item that has bounds that extend from a first predefined region to a second predefined region of the web page. The processor determines that one or more positions relative to the identified anchorable elements are usable for inserting a third-party content slot. The processor generates a list including positions relative to the identified anchorable elements determined to be usable.