c3-context-design

System boundaries establish the highest-level view of your architecture, clarifying what your system does, what it doesn't, and how its major deployable units (containers) interact. This Skill guides you through documenting container inventory, their responsibilities, communication protocols, and external actors, forming the foundational architecture that prevents scope creep and ensures alignment across teams.

Context-level architecture defines your system's boundary, external integrations, and major deployable units at the highest abstraction. Container-level architecture breaks those units into implementation details. Context design comes first—it establishes the foundational scope and interaction protocols that all lower architectural layers inherit and conform to.

This Skill helps you specify how different containers communicate—whether via REST, message queues, databases, or other protocols—and generates Mermaid diagrams to visualize these interactions. You define each protocol explicitly, analyze cross-container concerns, and document task scenarios like adding or removing containers to track how changes ripple through your system.

Yes. This Skill includes change-impact analysis to determine if a proposed modification truly belongs at the context level or should be delegated to a specific container. It prevents unnecessary system-wide ripple effects by helping you scope changes correctly before implementation.

A complete context document includes frontmatter with project settings, container inventory with responsibilities, documented interaction protocols between containers, identified external actors, cross-container concerns, and Mermaid diagrams showing system boundaries and major interactions. This Skill enforces mandatory section structure and verification guidelines to ensure nothing is missed.

When designing a new system, context-level architecture establishes scope upfront by identifying all external integrations, mapping primary deployable units, and defining communication channels. This foundational definition prevents downstream rework and ensures teams have shared understanding of system boundaries before diving into container-level or component-level design.