Mermaid

Mermaid.js v11

Overview

Create text-based diagrams using Mermaid.js v11 declarative syntax. Mermaid is the only diagram format that renders natively in GitHub markdown -- no exported images to commit.

Quick Start

Basic Diagram Structure:

{diagram-type}
  {diagram-content}

Common Diagram Types:

• flowchart - Process flows, decision trees
• sequenceDiagram - Actor interactions, API flows
• classDiagram - OOP structures, data models
• stateDiagram - State machines, workflows
• erDiagram - Database relationships
• gantt - Project timelines
• journey - User experience flows

WARNING: references/diagram-types.md covers all 24+ diagram types with full syntax. Load only when you need a specific type's syntax.

Creating Diagrams

Inline Markdown Code Blocks:

```mermaid
flowchart TD
    A[Start] --> B{Decision}
    B -->|Yes| C[Action]
    B -->|No| D[End]
```

Configuration via Frontmatter:

```mermaid
---
theme: dark
---
flowchart LR
    A --> B
```

Comments: Use %% prefix for single-line comments.

Syntax Rules

Follow these to avoid parse errors:

• Indentation: Use consistent 4-space indentation
• Node IDs: Short unique identifiers (A, B, node1). Avoid reserved words
• Special characters: Wrap text with special characters in quotes
• Subgraphs: Must close with end keyword
• Whitespace: No trailing whitespace (causes parsing failures)
• Complexity: Break diagrams at 15+ elements into multiple focused diagrams

CLI Usage

Convert .mmd files to images:

# Installation
npm install -g @mermaid-js/mermaid-cli

# Basic conversion
mmdc -i diagram.mmd -o diagram.svg

# With theme and background
mmdc -i input.mmd -o output.png -t dark -b transparent

# Custom styling
mmdc -i diagram.mmd --cssFile style.css -o output.svg

See references/cli-usage.md for Docker, batch processing, and advanced workflows.

Configuration & Theming

Common Options:

• theme: "default", "dark", "forest", "neutral", "base"
• look: "classic", "handDrawn"
• fontFamily: Custom font specification
• securityLevel: "strict", "loose", "antiscript"

See references/configuration.md for complete config options, theming, and customization.

Practical Patterns

Load references/examples.md for:

• Architecture diagrams
• API documentation flows
• Database schemas
• Project timelines
• State machines
• User journey maps

Resources

• references/diagram-types.md - Syntax for all 24+ diagram types
• references/configuration.md - Config, theming, accessibility
• references/cli-usage.md - CLI commands and workflows
• references/integration.md - JavaScript API and embedding
• references/examples.md - Practical patterns and use cases

See Also

• /excalidraw - For architecture diagrams where hand-drawn aesthetic and drag-and-drop editing matter
• /design - Design thinking applies to diagram composition and layout
• /prose - Diagram labels benefit from the same concision rules as prose

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