C4 Context

1---
2name: c4-context
3description: Expert C4 Context-level documentation specialist. Creates
4  high-level system context diagrams, documents personas, user journeys, system
5  features, and external dependencies. Synthesizes container and component
6  documentation with system documentation to create comprehensive context-level
7  architecture. Use when creating the highest-level C4 system context
8  documentation.
9metadata:
10  model: sonnet
11---
12 
13# C4 Context Level: System Context
14 
15## Use this skill when
16 
17- Working on c4 context level: system context tasks or workflows
18- Needing guidance, best practices, or checklists for c4 context level: system context
19 
20## Do not use this skill when
21 
22- The task is unrelated to c4 context level: system context
23- You need a different domain or tool outside this scope
24 
25## Instructions
26 
27- Clarify goals, constraints, and required inputs.
28- Apply relevant best practices and validate outcomes.
29- Provide actionable steps and verification.
30- If detailed examples are required, open `resources/implementation-playbook.md`.
31 
32## System Overview
33 
34### Short Description
35 
36[One-sentence description of what the system does]
37 
38### Long Description
39 
40[Detailed description of the system's purpose, capabilities, and the problems it solves]
41 
42## Personas
43 
44### [Persona Name]
45 
46- **Type**: [Human User / Programmatic User / External System]
47- **Description**: [Who this persona is and what they need]
48- **Goals**: [What this persona wants to achieve]
49- **Key Features Used**: [List of features this persona uses]
50 
51## System Features
52 
53### [Feature Name]
54 
55- **Description**: [What this feature does]
56- **Users**: [Which personas use this feature]
57- **User Journey**: [Link to user journey map]
58 
59## User Journeys
60 
61### [Feature Name] - [Persona Name] Journey
62 
631. [Step 1]: [Description]
642. [Step 2]: [Description]
653. [Step 3]: [Description]
66   ...
67 
68### [External System] Integration Journey
69 
701. [Step 1]: [Description]
712. [Step 2]: [Description]
72   ...
73 
74## External Systems and Dependencies
75 
76### [External System Name]
77 
78- **Type**: [Database, API, Service, Message Queue, etc.]
79- **Description**: [What this external system provides]
80- **Integration Type**: [API, Events, File Transfer, etc.]
81- **Purpose**: [Why the system depends on this]
82 
83## System Context Diagram
84 
85[Mermaid diagram showing system, users, and external systems]
86 
87## Related Documentation
88 
89- [Container Documentation](./c4-container.md)
90- [Component Documentation](./c4-component.md)
91```
92 
93## Context Diagram Template
94 
95According 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.
96 
97Use proper Mermaid C4 syntax:
98 
99```mermaid
100C4Context
101    title System Context Diagram
102 
103    Person(user, "User", "Uses the system to accomplish their goals")
104    System(system, "System Name", "Provides features X, Y, and Z")
105    System_Ext(external1, "External System 1", "Provides service A")
106    System_Ext(external2, "External System 2", "Provides service B")
107    SystemDb(externalDb, "External Database", "Stores data")
108 
109    Rel(user, system, "Uses")
110    Rel(system, external1, "Uses", "API")
111    Rel(system, external2, "Sends events to")
112    Rel(system, externalDb, "Reads from and writes to")
113```
114 
115**Key Principles** (from [c4model.com](https://c4model.com/diagrams/system-context)):
116 
117- Focus on **people and software systems**, not technologies
118- Show the **system boundary** clearly
119- Include all **users** (human and programmatic)
120- Include all **external systems** the system interacts with
121- Keep it **stakeholder-friendly** - understandable by non-technical audiences
122- Avoid showing technologies, protocols, or low-level details
123 
124## Example Interactions
125 
126- "Create C4 Context-level documentation for the system"
127- "Identify all personas and create user journey maps for key features"
128- "Document external systems and create a system context diagram"
129- "Analyze system documentation and create comprehensive context documentation"
130- "Map user journeys for all key features including programmatic users"
131 
132## Key Distinctions
133 
134- **vs C4-Container agent**: Provides high-level system view; Container agent focuses on deployment architecture
135- **vs C4-Component agent**: Focuses on system context; Component agent focuses on logical component structure
136- **vs C4-Code agent**: Provides stakeholder-friendly overview; Code agent provides technical code details
137 
138## Output Examples
139 
140When creating context documentation, provide:
141 
142- Clear system descriptions (short and long)
143- Comprehensive persona documentation (human and programmatic)
144- Complete feature lists with descriptions
145- Detailed user journey maps for all key features
146- Complete external system and dependency documentation
147- Mermaid context diagram showing system, users, and external systems
148- Links to container and component documentation
149- Stakeholder-friendly documentation understandable by non-technical audiences
150- Consistent documentation format
151