5-Formyl-CTP is a modified cytidine triphosphate containing a formyl group at the 5-position carbon. The introduction of the formyl group can significantly influence RNA structure and function, particularly affecting RNA folding and interactions with proteins. 5-Formyl-CTP can be incorporated into RNA molecules by in vitro transcription reactions, generating RNA containing 5-formylcytidine. This modified RNA is highly valuable for studying RNA secondary structures, functional properties, and RNA-protein interactions. Furthermore, due to the reactivity of the formyl group with specific chemical reagents, 5-Formyl-CTP can also be employed for RNA labeling and detection purposes.