| name | architecture-c4-modeling |
| description | C4 architecture modeling workflow for context, container, and component views that make boundaries and responsibilities explicit. Use when teams need a shared structural model before major implementation or refactoring; do not use as a substitute for decision records. |
Architecture C4 Modeling
Overview
Use this skill to produce C4 views that remove architectural ambiguity and help teams reason about scope, ownership, and risk.
Scope Boundaries
- System boundaries are unclear across teams or services.
- People disagree on where responsibilities belong.
- A large change requires shared architecture context before coding.
Core Judgments
- System boundary: what is inside the system and what is external dependency.
- Container split: what deserves a runtime boundary versus a module boundary.
- Component granularity: where decomposition clarifies behavior versus adds noise.
- Trust boundaries and data sensitivity: where stronger controls are required.
Practitioner Heuristics
- Each relationship in diagrams must answer one operational question: ownership, protocol, failure impact, or data-classification.
- If two boxes cannot be owned by different teams or deployed/scaled independently, they are usually not separate containers.
- Component diagrams are useful only for high-change or high-risk containers; do not draw them by default.
- Keep names consistent with runtime artifacts and code modules to avoid translation loss.
Workflow
- Define the audience and the questions each C4 level must answer.
- Draw the context view around real external actors and systems.
- Draw container boundaries based on runtime and ownership constraints.
- Add component views only where behavior is too complex for container-level reasoning.
- Annotate critical interactions with trust, latency, and failure assumptions.
- Reconcile naming and dependencies with actual repositories and runtime topology.
Common Failure Modes
- Diagrams mirror org charts instead of runtime behavior.
- Container boundaries are chosen by technology preference rather than coupling/ownership.
- Component diagrams become full class diagrams and lose decision value.
Failure Conditions
- Stop when source system inventory is stale or contradictory.
- Stop when critical boundaries cannot be represented unambiguously.
- Escalate when diagram conclusions conflict with approved architectural decisions.
