--- name: mermaid-diagrams model: fast version: 1.0.0 description: > Create software diagrams using Mermaid syntax. Use when users need to create, visualize, or document software through diagrams including class diagrams, sequence diagrams, flowcharts, ERDs, C4 architecture diagrams, state diagrams, git graphs, and other diagram types. Triggers include requests to diagram, visualize, model, map out, or show the flow of a system. tags: [diagrams, mermaid, visualization, architecture, documentation, modeling] ---

Mermaid Diagrams

Create professional software diagrams using Mermaid's text-based syntax. Mermaid renders diagrams from simple text definitions, making diagrams version-controllable, easy to update, and maintainable alongside code.

Installation

OpenClaw / Moltbot / Clawbot

npx clawhub@latest install mermaid-diagrams

Core Syntax

All Mermaid diagrams follow this pattern:

diagramType
  definition content

Key principles:

• First line declares diagram type (e.g., classDiagram, sequenceDiagram, flowchart)
• Use %% for comments
• Line breaks and indentation improve readability but aren't required
• Unknown words break diagrams; invalid parameters fail silently

Diagram Type Selection

| Type | Use For | Reference | |------|---------|-----------| | Class Diagrams | Domain modeling, OOP design, entity relationships | references/class-diagrams.md | | Sequence Diagrams | API flows, auth flows, component interactions | references/sequence-diagrams.md | | Flowcharts | Processes, algorithms, decision trees, user journeys | references/flowcharts.md | | ERD | Database schemas, table relationships, data modeling | references/erd-diagrams.md | | C4 Diagrams | System context, containers, components, architecture | references/c4-diagrams.md | | State Diagrams | State machines, lifecycle states | — | | Git Graphs | Branching strategies | — | | Gantt Charts | Project timelines, scheduling | — |

For styling, themes, and layout options: See references/advanced-features.md

Quick Start Examples

Class Diagram (Domain Model)

classDiagram
    Title -- Genre
    Title *-- Season
    Title *-- Review
    User --> Review : creates

    class Title {
        +string name
        +int releaseYear
        +play()
    }

    class Genre {
        +string name
        +getTopTitles()
    }

Sequence Diagram (API Flow)

sequenceDiagram
    participant User
    participant API
    participant Database

    User->>API: POST /login
    API->>Database: Query credentials
    Database-->>API: Return user data
    alt Valid credentials
        API-->>User: 200 OK + JWT token
    else Invalid credentials
        API-->>User: 401 Unauthorized
    end

Flowchart (User Journey)

flowchart TD
    Start([User visits site]) --> Auth{Authenticated?}
    Auth -->|No| Login[Show login page]
    Auth -->|Yes| Dashboard[Show dashboard]
    Login --> Creds[Enter credentials]
    Creds --> Validate{Valid?}
    Validate -->|Yes| Dashboard
    Validate -->|No| Error[Show error]
    Error --> Login

ERD (Database Schema)

erDiagram
    USER ||--o{ ORDER : places
    ORDER ||--|{ LINE_ITEM : contains
    PRODUCT ||--o{ LINE_ITEM : includes

    USER {
        int id PK
        string email UK
        string name
        datetime created_at
    }

    ORDER {
        int id PK
        int user_id FK
        decimal total
        datetime created_at
    }

Best Practices

1. Start simple — begin with core entities/components, add details incrementally
2. Use meaningful names — clear labels make diagrams self-documenting
3. Comment extensively — use %% comments to explain complex relationships
4. Keep focused — one diagram per concept; split large diagrams into multiple views
5. Version control — store .mmd files alongside code for easy updates
6. Add context — include titles and notes to explain diagram purpose
7. Iterate — refine diagrams as understanding evolves

Configuration and Theming

Configure diagrams using frontmatter:

---
config:
  theme: base
  themeVariables:
    primaryColor: "#ff6b6b"
---
flowchart LR
    A --> B

Available themes: default, forest, dark, neutral, base

Layout options:

• layout: dagre (default) — classic balanced layout
• layout: elk — advanced layout for complex diagrams

Look options:

• look: classic — traditional Mermaid style
• look: handDrawn — sketch-like appearance

Rendering and Export

Native support in:

• GitHub/GitLab — automatically renders in Markdown
• VS Code — with Markdown Mermaid extension
• Notion, Obsidian, Confluence — built-in support

Export options:

• Mermaid Live Editor — online editor with PNG/SVG export
• Mermaid CLI — npm install -g @mermaid-js/mermaid-cli then mmdc -i input.mmd -o output.png

When to Create Diagrams

Always diagram when:

• Starting new projects or features
• Documenting complex systems
• Explaining architecture decisions
• Designing database schemas
• Planning refactoring efforts
• Onboarding new team members

Use diagrams to:

• Align stakeholders on technical decisions
• Document domain models collaboratively
• Visualize data flows and system interactions
• Plan before coding
• Create living documentation that evolves with code

Common Pitfalls

• Breaking characters — avoid {} in comments; escape special characters
• Syntax errors — misspellings break diagrams; validate in Mermaid Live
• Overcomplexity — split complex diagrams into multiple focused views
• Missing relationships — document all important connections between entities
• Stale diagrams — a wrong diagram is worse than no diagram; update when systems change

NEVER Do

1. NEVER create diagrams with more than 15 nodes — they become unreadable; split into multiple focused diagrams
2. NEVER leave arrows unlabeled — every connection should explain the relationship or data flow
3. NEVER create diagrams without a title or caption — context-free diagrams are useless outside the author's head
4. NEVER use diagrams as the sole documentation — pair diagrams with prose that explains the "why"
5. NEVER let diagrams go stale — update diagrams when architecture changes; stale diagrams mislead
6. NEVER use Mermaid for data visualization — Mermaid is for architecture and flow diagrams, not charts of business data