Generate C4 System Context Diagrams and Documentation

This skill produces C4 model System Context-level documentation for a software system: a short and long system description, persona profiles for human, programmatic, or external-system users, each with type, description, goals, and key features used, a feature list linking each feature to the personas that use it, detailed user journey maps per feature-persona combination and for external-system integrations, a catalog of external systems and dependencies covering type, description, integration mechanism, and purpose, and a Mermaid C4Context diagram showing the system as a central box surrounded by its users and external systems, using proper syntax with Person, System, System_Ext, SystemDb, and Rel relationship declarations.

Use it when documenting a system's context level per the C4 model - identifying personas, mapping user journeys, cataloging external dependencies, or producing a system context diagram. It explicitly focuses on people and software systems, not technologies or protocols, so the output must stay stakeholder-friendly and understandable by non-technical audiences. Do not use it for tasks outside this scope, and distinguish it from sibling C4 skills: the Container agent covers deployment architecture, the Component agent covers logical component structure, and the Code agent covers technical code-level detail - this one stays at the highest, most abstract level.

Given a system to document, it produces a structured document covering the system overview with short and long descriptions, personas, features, user journeys, external systems and dependencies, and a Mermaid C4Context diagram, plus links out to Container and Component documentation for the next levels of detail. For deeper implementation guidance it references a companion resources/implementation-playbook.md file.

Mermaid's C4Context diagram syntax - Person, System, System_Ext, SystemDb, and Rel - is the primary rendering integration; the output is meant to link into a broader documentation set alongside Container- and Component-level docs. A typical Rel line documents both the relationship and its mechanism, for example a user "using" the system, the system "using" an external API, sending events to another external system, or reading from and writing to an external database.

Architects, tech leads, and documentation writers who need to produce or maintain the highest-level, stakeholder-facing view of a system - its users, external dependencies, and key user journeys - as the entry point into a fuller C4 documentation set. Typical requests this skill handles include creating context-level documentation for a system from scratch, identifying all personas and building user journey maps for key features, documenting external systems into a context diagram, or mapping journeys for programmatic as well as human users.