Chatbots are reactive applications with a conversational interface. They are usually implemented as compositions of client-side components and cloud-hosted services, including artificial-intelligence technology. Unfortunately, programming such reactive multi-tier applications with traditional programming languages is cumbersome. This paper introduces wcs-ocaml, a new multi-tier chatbot generator library designed for use with the reactive language ReactiveML. The paper explains our library with small didactic examples throughout, and closes with a larger case-study of a chatbot for authoring event-processing rules.