Mermaid Diagram to Image

Convert Mermaid diagrams to high-quality images in PNG, SVG, or PDF formats using the mermaid-cli tool.

When to Use This Skill

Activate this skill when:

• Generating Mermaid diagram syntax and wanting to provide a visual representation to the user
• Converting existing Mermaid diagrams (from files or discussion context) to image formats
• User requests diagram visualization in a specific format (PNG for embedding, SVG for web, PDF for print)

Quick Start

To convert a Mermaid diagram to an image:

1. Identify the source - Determine if working with diagram content, a file path, or inline Mermaid syntax
2. Create temporary file if needed - Use mktemp -t mermaid-XXXXXX.mmd for inline content
3. Run conversion - Execute mmdc with appropriate flags (input, output, dimensions, theme)
4. Clean up - Use rm -f /path/to/temp.mmd to remove temporary file
5. Report results - Confirm successful conversion with output filename

Conversion Workflow

Step 1: Parse Input

Determine the source of the Mermaid diagram:

• Diagram content in context - Mermaid syntax recently generated or discussed
• File path - User provides a path to a .mmd or .md file
• Inline Mermaid content - Raw Mermaid syntax provided by user
• Format preferences - User specifies output format (PNG, SVG, PDF) and options

Step 2: Set Up Variables

Establish conversion parameters with sensible defaults:

Output Format

• Default: png
• Options: png, svg, pdf

Output Filename

• Default pattern: mermaid-diagram-{SHORT_DESCRIPTIVE_NAME}
• Example: mermaid-diagram-flowchart.png, mermaid-diagram-sequence.svg
• Base name on diagram type or content context

Default Image Settings (High Resolution)

• Width: 1600 pixels
• Height: 1200 pixels
• Scale: 2 (for crisp rendering)

Optional Parameters

• Theme: default, forest, dark, neutral
• Background color: hex code or named color (e.g., transparent, white, #f0f0f0)
• PDF fit: -f flag for PDF output

Step 3: Handle Input

If file path provided:

• Verify file exists using Read or Glob tools
• Confirm file extension is .mmd or .md
• Use file path directly in mmdc command

If Mermaid content provided:

• Create temporary file: TEMP_FILE=$(mktemp -t mermaid-XXXXXX.mmd)
• Write diagram content to file using heredoc or echo
• Store temp file path for cleanup after conversion

Example:

TEMP_FILE=$(mktemp -t mermaid-XXXXXX.mmd)
cat > "$TEMP_FILE" << 'EOF'
graph TD
    A[Start] --> B[Process]
    B --> C[End]
EOF

Step 4: Construct mmdc Command

Build the mermaid-cli command with appropriate flags:

Required Flags

• -i <input-file> - Input file (temp file or user-provided file)
• -o <output-file> - Output file with appropriate extension

High Resolution Flags

• -w 1600 - Width in pixels (default for quality output)
• -H 1200 - Height in pixels (default for quality output)
• -s 2 - Scale factor (2x for high resolution)

Optional Flags

• -t <theme> - Theme selection (default, forest, dark, neutral)
• -b <color> - Background color (hex or named)
• -f - Fit to page (PDF output only)

Example Commands

PNG conversion (default):

mmdc -i diagram.mmd -o output.png -w 1600 -H 1200 -s 2

SVG with dark theme:

mmdc -i diagram.mmd -o output.svg -t dark -b transparent

PDF with fit:

mmdc -i diagram.mmd -o output.pdf -f -w 1600 -H 1200

Step 5: Execute and Clean Up

Execution

1. Run the constructed mmdc command using Bash tool
2. Capture output and error messages
3. Check exit code for success

Cleanup (if temporary file created)

1. Remove temporary file: rm -f "$TEMP_FILE"
2. Verify file is in temp directory (e.g., /tmp/ or /var/folders/) before deletion
3. Use -f flag to avoid errors if file doesn't exist

Verification

1. Confirm output file was created
2. Report success with output filename and location
3. If applicable, note image specifications (format, dimensions)

Step 6: Report Results

Provide clear feedback to user:

Success Message Template

Successfully converted Mermaid diagram to {format}.
Output: {filename}
Dimensions: {width}x{height}
Theme: {theme}

Error Handling

• If mmdc fails, report error message from stderr
• Common issues: invalid Mermaid syntax, missing dependencies, file permissions
• Suggest fixes: validate syntax, check mmdc installation, verify write permissions

Default Settings

Apply these defaults for high-quality output:

• Format: PNG
• Width: 1600 pixels
• Height: 1200 pixels
• Scale: 2 (for crisp rendering)
• Theme: default
• Filename pattern: mermaid-diagram-{descriptive-name}

Override defaults based on user requirements or diagram characteristics.

Common Scenarios

Scenario 1: Generate and visualize

1. Generate Mermaid diagram syntax based on user request
2. Create temporary file using mktemp -t mermaid-XXXXXX.mmd
3. Write diagram content to temporary file
4. Convert to PNG with default high-resolution settings
5. Present image to user
6. Clean up temporary file with rm -f

Scenario 2: Convert existing file

1. User provides file path to .mmd or .md file
2. Verify file exists and read content
3. Convert directly using file path
4. Output image file in same directory or user-specified location

Scenario 3: Custom format and styling

1. User requests SVG with dark theme and transparent background
2. Parse requirements
3. Construct mmdc command with theme and background flags
4. Execute conversion
5. Confirm output meets specifications

Theme Options

Available themes for customization:

• default - Standard blue/gray Mermaid theme
• forest - Green-themed palette
• dark - Dark background with light text
• neutral - Neutral gray tones

Apply theme with -t flag: mmdc -i input.mmd -o output.png -t dark

Mermaid Syntax Recognition

Recognize Mermaid diagrams by these starting keywords:

• graph or flowchart - Flowchart diagrams
• sequenceDiagram - Sequence diagrams
• classDiagram - Class diagrams
• stateDiagram - State diagrams
• erDiagram - Entity relationship diagrams
• gantt - Gantt charts
• pie - Pie charts
• journey - User journey diagrams
• gitGraph - Git graphs
• mindmap - Mind maps
• timeline - Timeline diagrams

Troubleshooting

mmdc command not found:

• Verify mermaid-cli is installed: npm list -g @mermaid-js/mermaid-cli
• Install if missing: npm install -g @mermaid-js/mermaid-cli

Syntax errors in diagram:

• Validate Mermaid syntax at https://mermaid.live
• Check for missing spaces, invalid keywords, or malformed connections
• Review Mermaid documentation for diagram-specific syntax

Output file not created:

• Verify write permissions in output directory
• Check disk space availability
• Ensure output path is valid

Image quality issues:

• Increase width/height for larger diagrams
• Adjust scale factor (try 3 for extra high resolution)
• Use SVG format for lossless scaling

Best Practices

1. Proactive conversion - When generating Mermaid diagrams, automatically convert to images for better user experience
2. Format selection - Choose PNG for general use, SVG for web/scaling needs, PDF for documents
3. High resolution - Use default high-resolution settings (1600x1200, scale 2) for quality output
4. Descriptive naming - Name output files based on diagram type or content for easy identification
5. Cleanup - Always clean up temporary files after successful conversion
6. Error reporting - Provide clear error messages with actionable troubleshooting steps