Generate C4 System Context Diagrams and Documentation

This skill produces C4 model System Context documentation, the highest-level of the four C4 levels: a short and long description of what the system does, its personas (human users, programmatic users, or external systems, each with their type, goals, and key features used), its features with the personas that use them, step-by-step user journeys per feature and persona, and its external systems and dependencies (type, integration method such as API/events/file transfer, and why the system depends on each one). It draws a system context diagram with Mermaid's C4Context syntax, placing the system as a box in the center surrounded by Person actors, System_Ext external systems, and SystemDb external databases, connected by Rel relationships describing how each one is used.

Use it to produce a high-level, stakeholder-friendly view of a system: who uses it, what it does, and which external systems it depends on - understandable by non-technical audiences. It does not apply outside C4 context-level documentation - a different domain or tool is out of scope. Per the C4 model's own stated principles for a system context diagram: focus on people and software systems rather than technologies or protocols, show the system boundary clearly, include all users (human and programmatic), include all external systems the system interacts with, and avoid low-level technical detail so the diagram stays understandable by non-technical stakeholders. It is distinct from three related C4 skills: a Container-level skill documents deployment architecture rather than the high-level system view, a Component-level skill documents logical component structure rather than system context, and a Code-level skill provides technical code detail rather than a stakeholder-friendly overview.

Inputs: a description of the system's purpose and capabilities, its user personas, its key features, and the external systems, databases, or services it integrates with. Outputs: a short and long system description, persona documentation for human and programmatic users, a feature list linked to user journey maps, complete external-system and dependency documentation, a Mermaid C4Context diagram of the system, its users, and external systems, and links to the corresponding container and component documentation.

Mermaid's C4Context diagram syntax (Person, System, System_Ext, SystemDb, Rel), rendered as the top level of the C4 model, above container, component, and code.

C4Context
    title System Context Diagram

    Person(user, "User", "Uses the system to accomplish their goals")
    System(system, "System Name", "Provides features X, Y, and Z")

Architects and technical writers producing a stakeholder-friendly overview of a system - its users, features, user journeys, and external dependencies - as the entry point into the more detailed C4 container, component, and code levels.