C4 diagrams

Draw software architecture as a small set of maps at different zoom levels, one abstraction per map. Based on Simon Brown's C4 model and Software Architecture for Developers. The point is communication: each diagram tells a different part of the same story to a different audience, and each one stands on its own without a narrative.

Not this skill (use instead)

• Domain modelling, ports/adapters, error design -> architecture skill. This skill draws and verifies the model; that one decides what to model.
• Decision rationale, ADRs, keeping docs from rotting -> living-documentation skill. C4 shows static structure; the why belongs in ADRs/a guidebook.
• Behaviour: business processes, workflows, state, data models. C4 is static structure only. Use BPMN / UML state / sequence / ER instead.

The core in 30 seconds (sticky rules)