Free AI UML Diagram Generator For Mermaid, PlantUML, And Draw.io
Create, edit, preview, and export diagrams in one workspace with AI-assisted Mermaid, PlantUML, and Draw.io workflows
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Create diagrams through conversation or directly edit Mermaid, PlantUML, or Draw.io content
Choose The Right Mode For Your Diagram
OnUML supports Mermaid live editor workflows, PlantUML online editor workflows, and Draw.io editor workflows in one place.
Choose the right mode based on how you work. Mermaid is ideal for quick docs and lightweight diagrams, PlantUML fits formal UML and technical modeling, and Draw.io editor flows are better for visual architecture, whiteboard planning, and collaborative editing.
Mermaid
A lightweight text DSL with markdown-style syntax for fast documentation-driven diagrams.
Characteristics
A lightweight text DSL with markdown-style syntax for fast documentation-driven diagrams.
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The biggest strength of Mermaid is simplicity. It is lightweight, the easiest to learn, visually modern, and especially effective when you want diagrams to live directly inside Markdown content.
Supported diagram types
- Flowchart
- Sequence
- Gantt
- State
- Basic ER
PlantUML
An engineering-oriented text DSL for formal UML and complex architecture modeling.
Characteristics
An engineering-oriented text DSL for formal UML and complex architecture modeling.
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Compared with Mermaid, PlantUML supports a wider range of complex and formal diagram types. The tradeoff is that the code is usually more detailed and more complex to write.
Supported diagram types
- Class
- Sequence
- Use Case
- Component
- Deployment
- C4
Draw.io
A visual drag-and-drop editor for freeform diagrams, presentation visuals, and whiteboard-style layouts.
Characteristics
A visual drag-and-drop editor for freeform diagrams, presentation visuals, and whiteboard-style layouts.
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Compared with Mermaid and PlantUML, Draw.io stands out for direct drag-and-drop editing in the UI. It offers the highest layout freedom across many diagram styles and requires no coding at all.
Supported diagram types
- Architecture Diagram
- Flowchart
- UML
- Org Chart
- Network Diagram
- Whiteboard Layout
Code Example + Rendered Result
Compare how each mode looks before opening the full editor.
Code Example
flowchart LR
A[Idea] --> B[Mermaid Live Editor]
B --> C[Quick Docs]
B --> D[Sequence]
B --> E[Mindmap]Rendered Result
One Workspace For Text Diagrams And Visual Canvas Editing
Use chat to diagram, code-based editing, visual canvas editing, and export/share/history workflows in one AI UML diagram generator
How The Three-Mode Workflow Works
Go from idea to diagram by choosing the right mode, refining the content, and exporting the result
Start with a prompt, a rough structure, or a template when you need a faster first draft
Use Mermaid for quick docs, PlantUML for formal UML, or Draw.io for architecture and whiteboard style diagrams
Refine the diagram, preview changes instantly, then export or share the result when it is ready
Frequently Asked Questions
Learn more about using OnUML
Will my chat content be used for AI training?
Your chat content is encrypted and never used for AI training
Are there any usage limits?
Reasonable usage limits ensure service quality
What types of UML diagrams are supported?
OnUML supports all standard UML diagrams including class diagrams, sequence diagrams, use case diagrams, activity diagrams, state diagrams, component diagrams, and deployment diagrams.
How can I save my diagrams?
You can export diagrams as PNG, SVG. You can also save your diagrams to your account for future access and editing if you create a free account.
What is the difference between Mermaid, PlantUML, and Draw.io?
Mermaid is optimized for fast text-based diagrams in docs, PlantUML is stronger for formal UML and structured technical modeling, and Draw.io is better for visual canvas editing, architecture maps, and collaborative whiteboard-style work.
Which mode should I choose for system design, UML, or whiteboard diagrams?
Choose Mermaid for quick documentation diagrams, PlantUML for formal UML design, and Draw.io for architecture overviews, whiteboards, and visual layout-heavy diagrams.