PyMMDC - Pure Python Mermaid Diagram Converter

A robust, local-only Mermaid to PNG converter with comprehensive Markdown processing support. Convert Mermaid diagrams seamlessly without any web requests or external dependencies beyond your local Mermaid CLI installation.

🚀 Key Features

• 🔒 Pure Local Operation: No web requests - exclusively uses local Mermaid CLI
• 🛡️ Robust Error Handling: Comprehensive exception hierarchy with detailed error messages and validation
• 📄 Markdown File Processing: Automatically detects and processes Mermaid code blocks in .md files
• ⚙️ Flexible Configuration: Customizable diagram appearance (themes, sizes, backgrounds)
• 🔄 Batch Processing: Convert multiple files and directories with single commands
• 📝 Metadata Support: Configure diagrams using code block metadata
• 🧹 Resource Management: Proper temporary file cleanup with context manager support
• 📊 Detailed Reporting: Structured results with execution metrics and success rates

📦 Installation

Prerequisites

1. Node.js (v14 or higher) - Download here
2. Mermaid CLI:

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

Install PyMMDC

pip install pymmdc

🎯 Quick Start

Command Line Interface

# Convert single Mermaid file
pymmdc diagram.mmd diagram.png

# Process Markdown file with Mermaid blocks
pymmdc document.md --output-dir ./images

# Batch process multiple Markdown files
pymmdc "docs/*.md" --batch --output-dir ./generated_images

# Replace Mermaid blocks with images in output
pymmdc README.md --replace-blocks --output-dir ./assets

# Custom theme and dimensions
pymmdc diagram.mmd --theme dark --width 1600 --height 1200

Python API

from pymmdc import EnhancedMermaidConverter

# Simple conversion
with EnhancedMermaidConverter() as converter:
    result = converter.convert_file("diagram.mmd", "output.png")

# Markdown processing
result = converter.convert_file(
    "document.md",
    process_markdown=True,
    output_dir="./images",
    replace_blocks=True
)

# Batch processing
results = converter.batch_convert(["file1.md", "file2.mmd"])

📝 Usage Examples

Basic Mermaid Conversion

# Convert .mmd or .mermaid files to PNG
pymmdc flowchart.mmd flowchart.png
pymmdc sequence.mermaid sequence.png

Markdown Processing

Process Markdown files containing Mermaid code blocks:

# My Document

Here's a flowchart:

```mermaid
graph TD
    A[Start] --> B{Decision}
    B -->|Yes| C[Action 1]
    B -->|No| D[Action 2]
```

And a sequence diagram:

```mermaid
sequenceDiagram
    Alice->>Bob: Hello Bob!
    Bob-->>Alice: Hello Alice!
```

# Process all Mermaid blocks in Markdown
pymmdc document.md --output-dir ./diagrams

# Replace code blocks with images in new Markdown file
pymmdc document.md --replace-blocks --output-dir ./assets

Advanced Configuration

Use metadata in code blocks for per-diagram settings:

```mermaid { "theme": "dark", "width": 1600, "title": "System Architecture" }
graph TB
    subgraph Frontend
        A[Web App]
        B[Mobile App]
    end
    
    subgraph Backend
        C[API Server]
        D[Database]
    end
    
    A --> C
    B --> C
    C --> D
```

⚙️ Configuration Options

Command Line Flags

Supported Metadata

Configure diagrams using JSON metadata in code blocks:

{
  "theme": "dark",
  "width": 1600,
  "height": 900,
  "title": "My Diagram",
  "bgcolor": "white"
}

🔧 Advanced Usage

Batch Processing

# Process all Markdown files in a directory
pymmdc "project/docs/**/*.md" --batch --recursive --output-dir ./generated

# Dry run to see what would be processed
pymmdc "*.md" --batch --dry-run

# Custom output directory and theme
pymmdc "**/*.md" --batch --output-dir ./docs/assets --theme forest

Integration with Documentation Pipelines

# Pre-process documentation before building
pymmdc "docs/**/*.md" --batch --replace-blocks --output-dir docs/assets

# CI/CD integration example
pymmdc README.md --output-dir ./badges || echo "Diagram generation failed"

🐛 Troubleshooting

Common Issues

1. Mermaid CLI not found:

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

2. Node.js version too old:

   # Update Node.js
   npm install -g n
   n stable
   

3. Permission errors:

   # Ensure write permissions in output directory
   chmod +w ./output-directory
   

Debug Mode

Enable verbose logging for troubleshooting:

pymmdc document.md --verbose --output-dir ./debug

📊 Output Examples

Successful processing provides detailed reports:

Markdown Processing Complete!
File: document.md
Blocks found: 3
Blocks converted: 3
Success rate: 100.0%
Output files:
  - document_architecture.png
  - document_flowchart.png
  - document_sequence.png

🤝 Contributing

We welcome contributions! Please see our contributing guidelines for details.

📄 License

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.

See the LICENSE file for more details. See the LICENSE file for details.

🆘 Support

• 📚 Documentation
• 🐛 Issue Tracker
• 💬 Discussions

PyMMDC: Making Mermaid diagram conversion reliable, fast, and completely local. 🚀