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)

```mermaid
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

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

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

mermaid-diagrams

Mermaid Diagrams

Installation

OpenClaw / Moltbot / Clawbot

Core Syntax