PRISM is an interactive system design simulator for practicing distributed system architecture. The application allows users to build a system design by dragging components onto a canvas and connecting them, then sends simulated traffic through the architecture to observe its behavior under load. It identifies failure points such as single points of failure, database saturation, queue overload, latency spikes, replica lag, and throughput collapse, and shows which part of the system fails first and why. Users can run simulations without any setup and receive direct feedback on the consequences of each design decision. The tool scores every submitted design against a rubric of five criteria that reflect what interviewers at major technology companies evaluate in system design interviews. PRISM also demonstrates trade-offs that arise at scale, including scalability versus simplicity, consistency versus availability, latency versus throughput, cost versus reliability, and synchronous versus asynchronous processing. The simulations are designed to be run repeatedly, with each iteration allowing the user to fix identified weaknesses and resubmit an improved architecture. PRISM includes a System Design Roadmap that progresses through five phases, from fundamentals to production systems. The curriculum contains more than 20 concepts and 40 interview questions, representing approximately 25 hours of end-to-end material. Each concept is presented as a short explanation with an interactive diagram, followed by a hands-on exercise where the user applies the concept in a working architecture and tests it with simulated traffic. The typical workflow is iterative: design an architecture, simulate real traffic, receive a score with diagnostic feedback, then revise and repeat.