C4 Context

# C4 Context Level: System Context

Use this skill when

- Working on c4 context level: system context tasks or workflows

- Needing guidance, best practices, or checklists for c4 context level: system context

Do not use this skill when

- The task is unrelated to c4 context level: system context

- You need a different domain or tool outside this scope

Instructions

- Clarify goals, constraints, and required inputs.

- Apply relevant best practices and validate outcomes.

- Provide actionable steps and verification.

- If detailed examples are required, open `resources/implementation-playbook.md`.

System Overview

Short Description

[One-sentence description of what the system does]

Long Description

[Detailed description of the system's purpose, capabilities, and the problems it solves]

Personas

[Persona Name]

- **Type**: [Human User / Programmatic User / External System]

- **Description**: [Who this persona is and what they need]

- **Goals**: [What this persona wants to achieve]

- **Key Features Used**: [List of features this persona uses]

System Features

[Feature Name]

- **Description**: [What this feature does]

- **Users**: [Which personas use this feature]

- **User Journey**: [Link to user journey map]

User Journeys

[Feature Name] - [Persona Name] Journey

1. [Step 1]: [Description]

2. [Step 2]: [Description]

3. [Step 3]: [Description]

...

[External System] Integration Journey

1. [Step 1]: [Description]

2. [Step 2]: [Description]

...

External Systems and Dependencies

[External System Name]

- **Type**: [Database, API, Service, Message Queue, etc.]

- **Description**: [What this external system provides]

- **Integration Type**: [API, Events, File Transfer, etc.]

- **Purpose**: [Why the system depends on this]

System Context Diagram

[Mermaid diagram showing system, users, and external systems]

Related Documentation

- Container Documentation

- Component Documentation

## Context Diagram Template

According to the [C4 model](https://c4model.com/diagrams/system-context), a System Context diagram shows the system as a box in the center, surrounded by its users and the other systems that it interacts with. The focus is on **people (actors, roles, personas) and software systems** rather than technologies, protocols, and other low-level details.

Use proper Mermaid C4 syntax:

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")

System_Ext(external1, "External System 1", "Provides service A")

System_Ext(external2, "External System 2", "Provides service B")

SystemDb(externalDb, "External Database", "Stores data")

Rel(user, system, "Uses")

Rel(system, external1, "Uses", "API")

Rel(system, external2, "Sends events to")

Rel(system, externalDb, "Reads from and writes to")

**Key Principles** (from [c4model.com](https://c4model.com/diagrams/system-context)):

- Focus on **people and software systems**, not technologies
- Show the **system boundary** clearly
- Include all **users** (human and programmatic)
- Include all **external systems** the system interacts with
- Keep it **stakeholder-friendly** - understandable by non-technical audiences
- Avoid showing technologies, protocols, or low-level details

## Example Interactions

- "Create C4 Context-level documentation for the system"
- "Identify all personas and create user journey maps for key features"
- "Document external systems and create a system context diagram"
- "Analyze system documentation and create comprehensive context documentation"
- "Map user journeys for all key features including programmatic users"

## Key Distinctions

- **vs C4-Container agent**: Provides high-level system view; Container agent focuses on deployment architecture
- **vs C4-Component agent**: Focuses on system context; Component agent focuses on log