c4-context

SKILL.md

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

...

[External System] Integration Journey

...

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:

```mermaid
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):

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 logical component structure

vs C4-Code agent: Provides stakeholder-friendly overview; Code agent provides technical code details

Output Examples

When creating context documentation, provide:

Clear system descriptions (short and long)

Comprehensive persona documentation (human and programmatic)

Complete feature lists with descriptions

Detailed user journey maps for all key features

Complete external system and dependency documentation

Mermaid context diagram showing system, users, and external systems

Links to container and component documentation

Stakeholder-friendly documentation understandable by non-technical audiences

Consistent documentation format

Limitations

Use this skill only when the task clearly matches the scope described above.

Do not treat the output as a substitute for environment-specific validation, testing, or expert review.

Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.