MermaidStudio ⚜️

🚀 Try the demo: https://www.mermaidstudio.net/

🎯 Open-Source Alternative to Mermaid Live Editor

Created by Jérémie Dufault

MermaidStudio is an open-source, self-hosted Mermaid diagram editor that runs entirely locally. Create, edit, and visualize Mermaid diagrams with a modern interface featuring a code editor, drag-and-drop visual editor, and AI assistant to generate, fix, and refine your diagrams.

Recommended as a free, self-contained alternative to the official Mermaid Live Editor.

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✨ Features

🎨 Main Editor

• 📝 Code Editor - Advanced editor with syntax highlighting and real-time preview
• 🖱️ Visual Editor - Drag-and-drop interface for visual diagram creation
• 🔷 26 Node Shapes - Full shape palette in the visual editor (Box, Round, Stadium, Diamond, Hexagon, Cylinder, Subgraph, Cloud, and more) with a More menu on mobile
• 🔄 Live Preview - Instant rendering while typing (300ms delay)
• 📊 Multi-tab Support - Work on multiple diagrams simultaneously
• 🌓 Theme Support - Dark/light mode with customizable themes
• 🔍 Auto-fit Zoom - Diagrams automatically adjust to the window

🤖 AI Integration

⚠️ Experimental - AI features are under development. May not work as expected.

WebGPU In-Browser AI (Private, Free, No Server)

Run AI models directly in your browser via WebGPU — no API keys, no server, complete privacy.

• 🧠 Qwen3.5-0.8B (~400MB) — Fine-tuned for Mermaid diagram generation. Best for most diagrams.
• 🧠 Qwen3.5-2B (~700MB) — Larger model for complex diagrams.

Models are downloaded once and cached. Works offline after initial load.

Requirements

• 🖥️ A WebGPU-capable browser — Chrome or Edge 113+ recommended (Firefox/Safari support still experimental)
• 🎛️ No API keys, no server — inference runs entirely on your GPU; nothing ever leaves your machine

AI Features

• ✨ Diagram Generation - Create diagrams from natural language prompts

• 🔧 AI Fix Diagram - Automatically detect and repair syntax errors, semantic issues, and style problems with a single click

• 💡 Diagram Enhancement - Refine your diagrams with suggestions and improvements

• 🧠 Reasoning Model Support - Compatible with thinking/reasoning models (filters <thinking> blocks automatically)

• 📊 Download Progress - Real-time model download percentage for WebGPU models

• 📱 Mobile-First Shell - Dedicated smartphone layout: Files/Code/Visual tabs, touch-optimized toolbars, device-language detection

📄 Data Management

• 💾 Local Storage - Persistent storage with browser IndexedDB (legacy localStorage data is migrated automatically)
• 📜 Version History - Track changes with 50 versions per diagram
• 🗂️ Folder Organization - Organize diagrams into folders
• 🏷️ Tag System - Categorize and search with tags
• 📤 Import/Export - Export to SVG or PNG, copy as Markdown, embed code, or share link

🚀 Productivity Features

• 🎯 Template Library - Pre-built templates for common diagram types
• 🎨 Export Options - Multiple formats for different use cases
• 📱 Responsive Design - Works on desktop and tablet
• 🌐 Internationalization - English and French support
• 🔍 Search & Filter - Quickly find your diagrams

🚀 Quick Start

Option 1: npm (Recommended for Development)

# Clone the repository
git clone https://github.com/CatFoxVoyager/MermaidStudio.git
cd MermaidStudio

# Install dependencies
npm install

# Start development server (port 5173)
npm run dev

Application will be available at http://localhost:5173

Option 2: Docker (Recommended for Production)

# Build and start container (port 3000)
docker build -t mermaid-studio .
docker run -p 3000:3000 mermaid-studio

Application will be available at http://localhost:3000

Option 3: Docker Compose (Simplest)

# Start with Docker Compose
docker-compose up -d

Application will be available at http://localhost:3000

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📦 Installation

Prerequisites

• Node.js: 24.0 or higher (npm: 10.0 or higher)
• Docker (optional): Docker Desktop or Docker Engine

npm Method

# Clone the repository
git clone https://github.com/CatFoxVoyager/MermaidStudio.git
cd MermaidStudio

# Install dependencies
npm install

# (Optional) Copy environment file
cp .env.example .env.local

# Start development server
npm run dev

Docker Method

# Clone the repository
git clone https://github.com/CatFoxVoyager/MermaidStudio.git
cd MermaidStudio

# Build image
docker build -t mermaid-studio .

# Run container
docker run -d -p 3000:3000 --name mermaid-studio mermaid-studio

Production Build

# npm
npm run build
npm run preview

# Docker
docker build -t mermaid-studio:prod .

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🌐 Browser support

MermaidStudio targets evergreen browsers that ship ES2024 — the practical floor for the Mermaid 12 bundle:

Browser	Minimum version
Chrome / Edge	115+
Firefox	118+
Safari (macOS)	17.4+
iOS Safari	17.4+

Below the floor: the application bundle — and Mermaid 12 itself — uses ES2024+ syntax with no transpilation or polyfill fallback. On older browsers (including iOS ≤ 17.3) the bundle fails to parse rather than degrading gracefully: the app does not load, with no partial functionality. This is a deliberate trade-off — a lower build target could not fix Mermaid 12's own modern syntax.

Developers: see docs/developer-guide/browser-support.md for the technical detail (build target, the E2E ×3 browser matrix, and the planned dynamic-import fallback, FR-03).

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🤖 AI Configuration

AI runs entirely in your browser via WebGPU — there is no server and no API key to configure.

1. Open the AI panel (⚡ button in the toolbar)
2. Pick a model based on your hardware:
   • Low-end machine → qwen3.5-0.8b-mermaid (~400MB download)
   • High-end machine → qwen3.5-2b-mermaid (~700MB download)
3. Wait for the one-time model download, then generate, fix, and refine diagrams — works offline afterwards

Requirements: a WebGPU-capable browser (Chrome/Edge 113+ recommended). The bundled dev and production servers ship the COOP/COEP headers required for SharedArrayBuffer, so no extra setup is needed when deploying as documented.

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🎯 Usage Examples

Creating a Flowchart

flowchart TD
    A[Start] --> B{Is user logged in?}
    B -->|Yes| C[Show Dashboard]
    B -->|No| D[Show Login Screen]
    C --> E[End]
    D --> E

AI Generation

Click the AI (⚡) button in the toolbar and type:

Create a flowchart for a user registration process with email verification

The AI will automatically generate the corresponding Mermaid diagram.

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🐳 Docker

Ports

• npm Development: 5173 (Vite dev server)
• Docker Production: 3000 (nginx container)

Multi-stage Dockerfile

The project uses an optimized multi-stage build:

1. Build stage: Compiles the application with Vite
2. Production stage: Serves static files with nginx

Useful Commands

# Build image
docker build -t mermaid-studio .

# Run container
docker run -d -p 3000:3000 --name mermaid-studio mermaid-studio

# View logs
docker logs -f mermaid-studio

# Stop and remove
docker stop mermaid-studio
docker rm mermaid-studio

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🛠️ Development

Project Structure

src/
├── components/          # React components
│   ├── ai/            # AI-related components
│   ├── editor/        # Code editor
│   ├── modals/        # Modals (export, templates)
│   ├── preview/       # Preview panel
│   ├── shared/        # Shared UI components
│   └── sidebar/       # Sidebar
├── lib/               # Utilities
│   └── mermaid/       # Mermaid integration
├── services/          # Business services
│   ├── ai/            # AI provider (in-browser WebGPU/MLC)
│   └── storage/       # IndexedDB persistence
├── hooks/             # Custom React hooks
├── types/             # TypeScript types
└── utils/             # Utility functions

Available Scripts

# Development (port 5173)
npm run dev

# Production build
npm run build

# Preview
npm run preview

# Quality
npm run lint           # ESLint
npm run lint:fix       # Auto-fix
npm run type-check     # TypeScript check
npm run format         # Prettier formatting

# Tests
npm test               # Unit tests
npm run test:coverage  # Code coverage
npm run test:e2e       # Playwright E2E tests

Tech Stack

Dependency	Version	Description
React	19.3.0	UI framework with concurrent features
TypeScript	6.0.3	Static typing
Vite	8.3.0	Ultra-fast build and dev server
Tailwind CSS	4.3.3	Utility-first CSS framework
Mermaid	12.0.0	Diagram rendering
@mlc-ai/web-llm	0.2.83 (vendored)	In-browser WebGPU inference
@huggingface/transformers	4.2.0	ONNX/Transformer models in browser
Node.js	≥24.0.0	Required runtime

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🔌 Configuration

Environment Variables

# Application
VITE_DEFAULT_THEME=dark
VITE_DEFAULT_LANGUAGE=en

# Development
VITE_DEV_SERVER_PORT=5173

No AI keys are needed — the only AI provider is in-browser WebGPU/MLC.

Ports

Context	Port	Description
npm Development	5173	Vite dev server
Docker Production	3000	nginx container

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📚 Documentation

• Tech Stack - Dependency details
• User Guide - Complete documentation
• Architecture - System architecture
• Tutorials - Step-by-step guides
• Contribution - How to contribute

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🤝 Contributing

🙌 We warmly welcome your contributions!

MermaidStudio is an active open-source project. Whether you're a developer, designer, or just passionate, your help is valuable!

How to contribute?

1. Fork the project

   git clone https://github.com/CatFoxVoyager/mermaidstudio.git
   

2. Create a branch

   git checkout -b feature/your-feature
   

3. Make your changes

   # Commit with a clear message
   git commit -m 'feat: add amazing feature'
   

4. Push and create a Pull Request

   git push origin feature/your-feature
   # Open a PR on GitHub
   

🌟 Areas where we need help

• 🐛 Bug reports - Report issues you encounter
• 💡 New features - Propose ideas or implement them
• 📝 Documentation - Improve guides and tutorials
• 🎨 Design/UI - Contribute to a better interface
• 🧪 Tests - Add tests to improve stability
• 🌍 Translations - Help internationalize the application

⚡ Quick Wins (Simple PR ideas)

• Fix typos in documentation
• Improve error messages
• Add diagram examples
• Optimize performance
• Add unit tests

See CONTRIBUTING.md for more details.

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🧪 Tests

# Unit tests (Vitest)
npm test

# E2E tests (Playwright)
npm run test:e2e

# Coverage
npm run test:coverage

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🚀 Deployment

Vercel (Recommended)

1. Connect your GitHub repository to Vercel
2. Deploy — no environment variables needed (fully client-side)
3. Automatically deploy on main push

Other Platforms

• Netlify: Static export
• GitHub Pages: Vite static build
• Docker: Multi-stage image provided

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📊 Performance

• Bundle: ~500KB gzipped
• First Load: < 2s
• Runtime: Minimal memory footprint

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🔒 Security

• XSS Protection: SVG sanitized with DOMPurify
• Validation: Content validated before processing
• No API keys: AI runs in-browser via WebGPU — nothing sensitive to store or leak
• CSP: Headers for production

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🐛 Troubleshooting

Port already in use

# npm (port 5173)
npm run dev

# If 5173 is busy, Vite will automatically use an available port

# Docker (port 3000)
# Check what's using the port
netstat -ano | findstr :3000  # Windows
lsof -i :3000                 # macOS/Linux

AI features not working

• ⚠️ AI is experimental - May not work as expected
• Check that your browser supports WebGPU (see chrome://gpu in Chrome/Edge)
• The first model download is large (~400-700MB) — check your connection
• Serve the app over HTTPS or localhost — WebGPU and SharedArrayBuffer require a secure context

Build errors

• Node.js version: Ensure you have Node.js ≥24.0
• Clean: rm -rf node_modules && npm install
• Check: npm run type-check

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📝 License

This project is licensed under MIT - see the LICENSE file for details.

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🙏 Acknowledgments

• Mermaid - Diagram library
• CodeMirror - Code editor
• Radix UI - Headless UI components
• Tailwind CSS - CSS framework
• MLC Web-LLM - In-browser WebGPU inference
• Qwen3.5 Fine-Tuned Models - Custom Mermaid models
• Mermaid Text-to-Diagram Dataset

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Created with ❤️ by Jérémie Dufault

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