Methods, systems, and apparatus include computer programs encoded on a computer-readable storage medium, including a system that includes a synthesis subsystem that automatically creates components for inclusion in a creative. The synthesis subsystem includes one or more modules that receive, as input, crawled content or metadata known or identified by the content serving system, and produce, as an output, a synthesized component for inclusion in a prospective creative. The system further includes an evaluation subsystem that evaluates quality of each of the synthesized components generated by the synthesis subsystem to determine measurable quality as against a baseline quality level. The system further includes a serving subsystem that receives queries and selects relevant content items responsive to the queries including, for a given content item, identification of one or more synthesized components generated by the synthesis subsystem depending on the evaluation of the respective synthesized components by the evaluation subsystem.