Mermaid Diagram Generator

Generate professional diagrams using Mermaid.js syntax - from simple flowcharts to complex system diagrams.

Quick Start

Basic Flowchart

Generate a simple flowchart:

node scripts/generate_diagram.js \
  --type flowchart \
  --title "Simple Flow" \
  --code "graph TD; A[Start] --> B[Process]; B --> C[End]" \
  -o diagram.png

Sequence Diagram

Create a sequence diagram showing interactions:

node scripts/generate_diagram.js \
  --type sequence \
  --title "User Authentication" \
  --code "sequenceDiagram; Alice->>Bob: Hello Bob; Bob-->>Alice: Hi Alice" \
  -o sequence.png

Gantt Chart

Create a project timeline:

node scripts/generate_diagram.js \
  --type gantt \
  --title "Project Timeline" \
  --code "gantt; title A Gantt Diagram; dateFormat YYYY-MM-DD; section Section; A task :a1, 2024-01-01, 30d; Another task :after a1 , 20d" \
  -o gantt.png

Supported Diagram Types

1. Flowchart (flowchart)

graph TD
    A[Start] --> B{Decision}
    B -->|Yes| C[Option 1]
    B -->|No| D[Option 2]
    C --> E[End]
    D --> E

Use cases: Process flows, decision trees, workflow diagrams

2. Sequence Diagram (sequence)

sequenceDiagram
    participant Alice
    participant Bob
    Alice->>Bob: Hello Bob, how are you?
    Bob-->>Alice: I am good thanks!
    Alice->>Bob: Great!

Use cases: API interactions, system communication, user flows

3. Gantt Chart (gantt)

gantt
    title Project Timeline
    dateFormat YYYY-MM-DD
    section Development
    Design: des1, 2024-01-01, 10d
    Coding: des2, after des1, 20d
    Testing: des3, after des2, 10d

Use cases: Project planning, task scheduling, milestone tracking

4. Class Diagram (classDiagram)

classDiagram
    class Animal {
        +String name
        +eat()
    }
    class Dog {
        +bark()
    }
    Animal <|-- Dog

Use cases: Software architecture, data modeling, object-oriented design

5. State Diagram (stateDiagram)

stateDiagram-v2
    [*] --> Still
    Still --> [*]
    Still --> Moving
    Moving --> Still
    Moving --> Crash
    Crash --> [*]

Use cases: State machines, workflow states, lifecycle diagrams

6. ER Diagram (erDiagram)

erDiagram
    CUSTOMER ||--o{ ORDER : places
    ORDER ||--|{ LINE_ITEM : contains
    CUSTOMER }|..|{ DELIVERY_ADDRESS : uses

Use cases: Database design, data relationships, entity modeling

7. Pie Chart (pie)

pie title Pets adopted by volunteers
    "Dogs" : 386
    "Cats" : 85
    "Rats" : 15

Use cases: Data distribution, proportions, statistics

8. Mindmap (mindmap)

mindmap
  root((mindmap))
    Origins
      Long history
      ::icon(fa fa-book)
      Popularisation
        British popular psychology author Tony Buzan
    Research
      On effectiveness<br/>and features
      On Automatic creation
        Uses
            Creative techniques
            Strategic planning
            Argument mapping

Use cases: Brainstorming, idea organization, knowledge mapping

Advanced Features

Custom Themes

Apply different visual themes:

--theme default
# Available themes: default, forest, dark, neutral

# Or use custom colors:
--theme-config '{"themeVariables": {"primaryColor": "#ffcccc"}}'

Diagram Direction

Control flowchart direction:

# Left to right
graph LR
    A --> B

# Top to bottom (default)
graph TD
    A --> B

Styling

Apply custom styles:

graph TD
    A[Start] --> B[Process]
    style A fill:#f9f,stroke:#333,stroke-width:4px
    style B fill:#bbf,stroke:#333,stroke-width:2px

Data Formats

Flowchart Syntax

graph TD (Top Down)
graph LR (Left Right)
graph BT (Bottom Top)
graph RL (Right Left)

Sequence Diagram Syntax

sequenceDiagram
    participant A as Name
    A->>B: Message
    B-->>A: Response

Gantt Chart Syntax

gantt
    dateFormat YYYY-MM-DD
    section Section
    Task :id1, 2024-01-01, 30d

Requirements

• Node.js 18+ (for mmdc CLI)
• mermaid-cli: Install with npm install -g @mermaid-js/mermaid-cli

Installation

# Install mermaid CLI globally
npm install -g @mermaid-js/mermaid-cli

# Verify installation
mmdc --version

Output

Diagrams are saved as high-quality PNG files suitable for:

• Presentations
• Documentation
• Reports
• Wiki pages

Common Patterns

Subgraphs in Flowcharts

graph TD
    subgraph One
    A1 --> A2
    end
    subgraph Two
    B1 --> B2
    end

Loops and Alt in Sequence

sequenceDiagram
    loop Every day
        Alice->>Bob: Hello
    end
    alt Condition
        Bob-->>Alice: Yes
    else Another condition
        Bob-->>Alice: No
    end

Notes in Diagrams

graph LR
    A[Node A]
    Note for A[This is a note]
    A --- Note for A

Tips & Tricks

1. Keep it simple: Start with basic structure, then add details
2. Use comments: %% This is a comment for documentation
3. Test incrementally: Build complex diagrams step by step
4. Check syntax: Use mermaid live editor for syntax validation

Resources

• Mermaid Official Docs
• Mermaid Live Editor
• Mermaid Syntax Examples