The slow uptake of technology by mathematics teachers is in contrast with the rapid growth in the availability of different digital resources specifically designed to help teaching and learning mathematics. We refer to platforms that were designed to permit for mathematical communication between multiple users. We seek to explore the affordances of such digital platforms to support mathematics teachers who wish to integrate technology as part of their practice, when planning and enacting technology-based mathematical activity. Specifically, we ask: What are the affordances and constraints of the platforms that may support instrumentation and instrumentalization processes leading to the development of teacher's didactic instrument for planning and enacting a mathematical activity in a digital environment? The four platforms we chose for analysis are STEP, DESMOS, WIMS and Labomep. Our analysis shows on the one hand that the platforms afford support to the teacher while enacting technology-based mathematics activities. On the other hand, we suggest several components of didactic instrumental genesis that mathematics teachers need to develop in order to take benefit from digital platform affordances. These components include the ability to base decision-making on data gathered and visualised in dashboard embedded in learning management systems.