AI Diagram Generator - Free Online UML Diagram Tool | OnUML
Why Use an AI Diagram Generator?
Creating UML diagrams manually can be time-consuming and error-prone. An AI diagram generator like OnUML lets you describe what you want in natural language, and the AI generates the diagram code for you — instantly.
Key Benefits
- Speed: Generate complex diagrams in seconds, not minutes
- Accuracy: AI understands UML standards and generates correct syntax
- Flexibility: Support for Mermaid, PlantUML, and Draw.io formats
- Free: OnUML offers a generous free tier with no credit card required
Try it now
Visit the editor and type: "Create a sequence diagram for user login flow"
Supported Diagram Types
| Diagram Type | Mermaid | PlantUML | Best For |
|---|---|---|---|
| Class Diagram | ✅ | ✅ | Software architecture design |
| Sequence Diagram | ✅ | ✅ | API flows, system interactions |
| Use Case Diagram | ❌ | ✅ | Requirements modeling |
| Activity Diagram | ✅ | ✅ | Business process workflows |
| ER Diagram | ✅ | ✅ | Database schema design |
| State Diagram | ✅ | ✅ | State machine modeling |
Getting Started
- Go to the OnUML editor
- Describe your diagram in plain English
- The AI generates the diagram code
- Export as PNG, SVG, or copy the source code
Example: User Login Flow
Describe: "A sequence diagram showing user login with email, password, and two-factor authentication"
OnUML will generate a complete sequence diagram showing the User, Frontend, Auth Service, and Database interactions — ready to export and share.
Frequently Asked Questions
Is OnUML really free?
Yes! OnUML offers a free tier with daily credits. You can create and export diagrams without any payment.
Can I use it for commercial projects?
Absolutely. Diagrams created with OnUML are yours to use in any project, commercial or personal.
What's the difference between Mermaid and PlantUML?
Mermaid uses a simpler, Markdown-like syntax and renders in the browser. PlantUML is more powerful for complex diagrams (especially UML) but requires a server-side renderer. OnUML supports both, and you can switch anytime.