Building an industrial spoken dialogue system (SDS) requires several iterations of design, deployment, test, and evaluation phases. Most industrial SDS developers use a graphical tool to design dialogue strategies. They are critical to get good system performances, but their evaluation is not part of the design phase. We propose integrating dialogue logs into the design tool so that developers can jointly monitor call flows and their associated Key Performance Indicators (KPI). It drastically shortens the complete development cycle, and offers a new design experience. Orange Dialogue Design Studio (ODDS), our design tool, allows developers to design several alternatives and compare their relative performances. It helps the SDS developers to understand and analyse the user behaviour, with the assistance of a reinforcement learning algorithm. The SDS developers can thus confront the different KPI and control the further SDS choices by updating the call flow alternatives.