Mermaid Image Generator

Mermaid Image Generator

Convert Mermaid diagram syntax to PNG/SVG images using the mermaid.ink online rendering API. Zero dependencies - uses only Node.js built-in modules and curl.

Quick Start

# From a .mmd file
node scripts/mermaid-to-image.js diagram.mmd output.png

# From stdin
echo "flowchart LR; A --> B" | node scripts/mermaid-to-image.js - output.png

# Generate SVG instead
node scripts/mermaid-to-image.js diagram.mmd output.svg

When to Use This Skill

Use this skill when:

• User asks to "draw a diagram", "create a flowchart", "make a visual"
• User needs diagram images for PPTs, documentation, or presentations
• User wants to convert Mermaid code to shareable image files
• Local Mermaid CLI (mmdc) is unavailable or has dependency issues

Script Usage

Basic Conversion

node scripts/mermaid-to-image.js <input> <output>

Input options:

• File path: diagram.mmd
• Stdin: - (pipe Mermaid code directly)

Output format: Determined by file extension (.png or .svg)

Examples

Example 1: Convert file to PNG

node scripts/mermaid-to-image.js flowchart.mmd flowchart.png

Example 2: Pipe from stdin

cat <<EOF | node scripts/mermaid-to-image.js - sequence.png
sequenceDiagram
    Alice->>Bob: Hello
    Bob-->>Alice: Hi
EOF

Example 3: Generate SVG for web

node scripts/mermaid-to-image.js architecture.mmd architecture.svg

Mermaid Diagram Types

This skill supports all Mermaid diagram types:

Example Mermaid Code

Flowchart

flowchart LR
    A[Start] --> B{Decision}
    B -->|Yes| C[Action 1]
    B -->|No| D[Action 2]
    C --> E[End]
    D --> E

Sequence Diagram

sequenceDiagram
    participant User
    participant API
    participant Database
    
    User->>API: POST /login
    API->>Database: Query
    Database-->>API: Result
    API-->>User: Response

Class Diagram

classDiagram
    Animal <|-- Duck
    Animal <|-- Fish
    Animal: +int age
    Animal: +String gender
    Animal: +isMammal()

API Details

Service: mermaid.ink Endpoints:

• PNG: https://mermaid.ink/img/{base64_code}
• SVG: https://mermaid.ink/svg/{base64_code}

Advantages:

• ✅ No local dependencies (no Chrome/Puppeteer needed)
• ✅ Free and fast
• ✅ Returns high-quality PNG/SVG
• ✅ Works in headless environments

Limitations:

• Requires internet connection
• Diagram code is sent to external service (don't use for sensitive data)

Error Handling

The script handles common errors:

❌ File not found: diagram.mmd
❌ API request failed: 400 Bad Request
❌ Failed to connect to mermaid.ink: Connection timeout

Troubleshooting:

1. Check internet connectivity
2. Verify Mermaid syntax at https://mermaid.live
3. Ensure output directory exists (script creates it automatically)

Integration Pattern

When creating diagrams for users:

1. Write Mermaid code → Save to .mmd file or use stdin
2. Run conversion script → Generate PNG/SVG
3. Send/deliver image → Attach to response or save to specified location

Example workflow:

# 1. Create diagram
cat > openclaw-flow.mmd <<EOF
flowchart LR
    User --> OpenClaw
    OpenClaw --> Tools
EOF

# 2. Convert to image
node scripts/mermaid-to-image.js openclaw-flow.mmd openclaw-flow.png

# 3. Use the image (send via message, save, etc.)

Best Practices

1. Keep diagrams simple - Under 15 nodes for readability
2. Use meaningful labels - Self-documenting diagrams
3. Test syntax first - Validate at mermaid.live before converting
4. Choose format wisely - PNG for PPTs, SVG for web/docs
5. Add comments - Use %% for in-diagram documentation

Security Notes

• Diagram code is sent to mermaid.ink API
• Do not include sensitive information in diagrams
• For sensitive data, use local Mermaid CLI instead