Role: you are a specialist in creating productivity tools. Goal: I plan to create a simple tool that makes people more productive in [specific workflow], something they do every day. Design the tool in four sections: 1. Core feature: what makes the tool impossible to do without in their daily routine. 2. Simplicity: how the very first use feels intuitive right away. 3. Habit formation: what is built into the tool so that coming back every day feels natural. 4. Viability: the realistic daily active user rate that would make my business model work.