wbd-box-and-arrow-diagrams

Use rectangles for services, cylinders for databases, queue shapes for message buses, and clouds for external systems you don't own. Label every arrow with a verb describing the action, such as "queries" or "publishes", so readers understand each interaction.

The C4 model has four levels: System Context (whole system as one box for executives), Container (deployables like services and databases), Component (modules inside one service), and Code (classes). Pick the level matching your audience rather than combining all levels in one diagram.

Use solid arrows for synchronous requests and dashed or visually distinct arrows for asynchronous events. This distinction matters because sync calls couple availability between services, while async events let consumers lag without blocking the publisher.

No. UML is a formal specification most working engineers don't use. This project teaches the informal 80% convention of boxes, cylinders, arrows, and a few shared shapes that appear in real design docs and PR reviews.

Complete the whiteboard foundations project first so the five basic shapes are muscle memory — you should draw a clean rectangle and labeled arrow in about five seconds. You also need a whiteboard or a tool like Excalidraw.