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
Workflow Videos
Create Diagrams From Text Or Images
Explore four example workflows. OnUML supports text and image inputs, editable diagrams, mind maps, and one-click AI repair when diagram code breaks.
Draw.io diagrams with AI
Create flexible Draw.io diagrams from text, images, and other source materials with AI. OnUML turns your ideas into editable diagrams with rich built-in shapes, so you can drag, drop, connect, resize, and refine everything directly on the page.
PlantUML and Mermaid diagrams
Generate PlantUML and Mermaid diagrams quickly with AI, then refine them through prompts or code. OnUML renders changes in real time, so you can keep the diagram, source code, and AI editing flow together.
Professional mind maps
Unlike the mind map syntax inside PlantUML or Mermaid, OnUML supports a professional mind map diagram type built for structured thinking. Create and refine mind maps with AI, then add, move, and edit nodes directly on the page without switching back to code.
AI diagram code repair
When PlantUML or Mermaid code has syntax errors, paste it into the code editor and repair it with one click. OnUML helps fix broken diagram code quickly so you can render and continue editing without manual debugging.
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
Core Features Of The AI UML Diagram Generator
Support Mermaid, PlantUML, and Draw.io for online generation, editing, repair, live rendering, version recovery, categorized saving, and export sharing
Project plans and AI credits
Pro increases account capacity for projects, workspaces, and image upload. Credits stay separate as an AI usage add-on.
Pro Monthly
Unlock image upload, expanded project capacity, and workspaces with a monthly subscription.
Pro Yearly
Unlock image upload, expanded project capacity, and workspaces with a yearly subscription.
| Capability | Free | Pro Monthly | Pro Yearly |
|---|---|---|---|
| Diagrams per project | 2 diagrams | 10 diagrams | 10 diagrams |
| Cloud projects per workspace | 10 projects | Unlimited | Unlimited |
| Workspaces | 2 workspaces | Unlimited | Unlimited |
| Image upload | Not included | Included | Included |
| Free model requests | 10 per day | No daily limit | No daily limit |
| Monthly included credits | None | 500 credits | 500 credits |
| Repair | Fixed credit cost | Fixed credit cost | Fixed credit cost |
AI usage add-on credits
Buy credits for extra AI generation, image understanding, premium model runs, and fixed-cost Repair. Credits do not unlock diagrams, project, workspace.
Credits expire 6 months after they are issued.
Create And Deliver UML Diagrams In Three Steps
Choose the right mode first, describe what you need, then refine and export or share the final result
Pick the mode that fits your diagram type and workflow. Use Mermaid for quick docs, PlantUML for formal UML, or Draw.io for architecture and whiteboard-style diagrams
Use a prompt, rough structure, or template to generate a first draft faster and avoid starting from scratch
Refine the diagram, check the rendered result in real time, then export PNG or SVG files or share the finished diagram with a link
Frequently Asked Questions
Quickly learn about OnUML's core capabilities, how it works, and pricing
What is OnUML?
OnUML is an AI UML diagram tool that brings together Mermaid, PlantUML, and Draw.io. It helps you quickly create, edit, and export diagrams through natural language, image input, or visual editing, while also supporting one-click code repair, version history, project-based organization, and one-click diagram sharing.
Are there any usage limits?
OnUML has reasonable usage limits to keep the service stable and the overall experience consistent. For most regular users, day-to-day use will not be affected.
What diagram types are supported?
OnUML currently supports Mermaid, PlantUML, and Draw.io, and lets you create, edit, preview, and switch between them conveniently in a single workspace.
How can I save my diagrams?
You can export diagrams as PNG, SVG, and other formats. If you create an account, you can also save diagrams by project for easier access, management, and continued editing later.
What is the difference between Mermaid, PlantUML, and Draw.io?
Mermaid is better for fast text-based diagrams and documentation visuals, PlantUML is better for formal UML and structured technical modeling, and Draw.io is better for visual canvas editing, architecture diagrams, and whiteboard collaboration.
Is OnUML free?
Most OnUML features are free and are enough for regular day-to-day use. Only a small number of advanced features require payment.