Wizard-of-Oz (WoZ) is a common technique enabling HRI researchers to explore aspects of interaction not yet backed by autonomous systems. A standardized, open, and flexible WoZ framework could therefore serve the community and accelerate research both for the design of robotic systems and for their evaluation. This paper presents the definition of OpenWoZ, a Wizard-of-Oz framework for HRI, designed to be updated during operation by the researcher controlling the robot. OpenWoZ is implemented as a thin HTTP server running on the robot, and a cloud-backed multi-platform client schema. The WoZ server accepts representational state transfer (REST) requests from a number and variety of clients simultaneously. This “separation of concerns” in OpenWoZ allows addition of commands, new sequencing of behaviors, and adjustment of parameters, all during run-time.