C4 Component

1---
2name: c4-component
3description: Expert C4 Component-level documentation specialist. Synthesizes C4
4  Code-level documentation into Component-level architecture, defining component
5  boundaries, interfaces, and relationships. Creates component diagrams and
6  documentation. Use when synthesizing code-level documentation into logical
7  components.
8metadata:
9  model: sonnet
10---
11 
12# C4 Component Level: [Component Name]
13 
14## Use this skill when
15 
16- Working on c4 component level: [component name] tasks or workflows
17- Needing guidance, best practices, or checklists for c4 component level: [component name]
18 
19## Do not use this skill when
20 
21- The task is unrelated to c4 component level: [component name]
22- You need a different domain or tool outside this scope
23 
24## Instructions
25 
26- Clarify goals, constraints, and required inputs.
27- Apply relevant best practices and validate outcomes.
28- Provide actionable steps and verification.
29- If detailed examples are required, open `resources/implementation-playbook.md`.
30 
31## Overview
32 
33- **Name**: [Component name]
34- **Description**: [Short description of component purpose]
35- **Type**: [Component type: Application, Service, Library, etc.]
36- **Technology**: [Primary technologies used]
37 
38## Purpose
39 
40[Detailed description of what this component does and what problems it solves]
41 
42## Software Features
43 
44- [Feature 1]: [Description]
45- [Feature 2]: [Description]
46- [Feature 3]: [Description]
47 
48## Code Elements
49 
50This component contains the following code-level elements:
51 
52- [c4-code-file-1.md](./c4-code-file-1.md) - [Description]
53- [c4-code-file-2.md](./c4-code-file-2.md) - [Description]
54 
55## Interfaces
56 
57### [Interface Name]
58 
59- **Protocol**: [REST/GraphQL/gRPC/Events/etc.]
60- **Description**: [What this interface provides]
61- **Operations**:
62  - `operationName(params): ReturnType` - [Description]
63 
64## Dependencies
65 
66### Components Used
67 
68- [Component Name]: [How it's used]
69 
70### External Systems
71 
72- [External System]: [How it's used]
73 
74## Component Diagram
75 
76Use proper Mermaid C4Component syntax. Component diagrams show components **within a single container**:
77 
78```mermaid
79C4Component
80    title Component Diagram for [Container Name]
81 
82    Container_Boundary(container, "Container Name") {
83        Component(component1, "Component 1", "Type", "Description")
84        Component(component2, "Component 2", "Type", "Description")
85        ComponentDb(component3, "Component 3", "Database", "Description")
86    }
87    Container_Ext(externalContainer, "External Container", "Description")
88    System_Ext(externalSystem, "External System", "Description")
89 
90    Rel(component1, component2, "Uses")
91    Rel(component2, component3, "Reads from and writes to")
92    Rel(component1, externalContainer, "Uses", "API")
93    Rel(component2, externalSystem, "Uses", "API")
94```
95````
96 
97**Key Principles** (from [c4model.com](https://c4model.com/diagrams/component)):
98 
99- Show components **within a single container** (zoom into one container)
100- Focus on **logical components** and their responsibilities
101- Show **component interfaces** (what they expose)
102- Show how components **interact** with each other
103- Include **external dependencies** (other containers, external systems)
104 
105````
106 
107## Master Component Index Template
108 
109```markdown
110# C4 Component Level: System Overview
111 
112## System Components
113 
114### [Component 1]
115- **Name**: [Component name]
116- **Description**: [Short description]
117- **Documentation**: [c4-component-name-1.md](./c4-component-name-1.md)
118 
119### [Component 2]
120- **Name**: [Component name]
121- **Description**: [Short description]
122- **Documentation**: [c4-component-name-2.md](./c4-component-name-2.md)
123 
124## Component Relationships
125[Mermaid diagram showing all components and their relationships]
126````
127 
128## Example Interactions
129 
130- "Synthesize all c4-code-\*.md files into logical components"
131- "Define component boundaries for the authentication and authorization code"
132- "Create component-level documentation for the API layer"
133- "Identify component interfaces and create component diagrams"
134- "Group database access code into components and document their relationships"
135 
136## Key Distinctions
137 
138- **vs C4-Code agent**: Synthesizes multiple code files into components; Code agent documents individual code elements
139- **vs C4-Container agent**: Focuses on logical grouping; Container agent maps components to deployment units
140- **vs C4-Context agent**: Provides component-level detail; Context agent creates high-level system diagrams
141 
142## Output Examples
143 
144When synthesizing components, provide:
145 
146- Clear component boundaries with rationale
147- Descriptive component names and purposes
148- Comprehensive feature lists for each component
149- Complete interface documentation with protocols and operations
150- Links to all contained c4-code-\*.md files
151- Mermaid component diagrams showing relationships
152- Master component index with all components
153- Consistent documentation format across all components
154