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name: system-design description: Create and manage system design diagrams with Mermaid. Use for architecture, flows, data models, and business logic visualization. allowed-tools: Read, Write, Glob, Bash

System Design Skill

Create Mermaid diagrams for System Design and Architecture.

Directory

Copy.concepts/
├── architecture/     # C4, Deployment, Infrastructure
├── flows/            # Auth, Data, User Journey
└── data-models/      # ER, Class, State Diagrams

Workflow

1. Analyze request: What needs to be visualized?
2. Choose diagram type: Appropriate for the use case
3. Document business logic: Text before diagram
4. Create Mermaid: Syntactically correct
5. Save in .concepts/: Correct category

Diagram Types

Architecture

• C4Context: System overview with actors
• C4Container: Technical containers (services)
• Flowchart: Deployment, Infrastructure

Flows

• Sequence: API calls, service interactions
• Flowchart: Processes, decisions
• State: Object states, state machines
• User Journey: UX flows

Data Models

• ER Diagram: Database relations
• Class Diagram: Domain models
• Mind Map: Hierarchies, brainstorming

Template

Copy# [Title]

## Business Context

[Description of business logic]

## [Diagram Name]

\`\`\`mermaid
[Diagram Code]
\`\`\`

## Details

[Tables, explanations, etc.]

Mermaid Syntax Quick Reference

Flowchart

Copyflowchart TD
    A[Start] --> B{Decision}
    B -->|Yes| C[Action]
    B -->|No| D[Other]

Sequence

CopysequenceDiagram
    A->>B: Request
    B-->>A: Response

ER Diagram

CopyerDiagram
    ENTITY1 ||--o{ ENTITY2 : relationship

State Diagram

CopystateDiagram-v2
    [*] --> State1
    State1 --> State2: event

C4 Context

CopyC4Context
    Person(user, "User")
    System(app, "App")
    Rel(user, app, "Uses")

File Naming

• kebab-case.md
• Descriptive name
• Use category folders

Examples:

• .concepts/architecture/deployment.md
• .concepts/flows/auth-flow.md
• .concepts/data-models/er-diagram.md