Free UML Diagram Generator Online
Create professional UML diagrams instantly with our free online UML diagram generator. Design class diagrams, sequence diagrams, use case diagrams, and activity diagrams with an intuitive drag-and-drop interface. Perfect for software architecture, documentation, and team collaboration.
UML Diagram Types
Class Diagrams
Model class structures, relationships, and hierarchies in object-oriented designs.
Sequence Diagrams
Visualize object interactions and message flows over time.
Use Case Diagrams
Capture system functionality from the user's perspective.
Activity Diagrams
Model workflow and process logic with decision points and parallel activities.
Component Diagrams
Show organizational structure of system components and dependencies.
Deployment Diagrams
Visualize hardware and software deployment architecture.
How to Create UML Diagrams
- Select diagram type - Choose from class, sequence, use case, or activity diagrams
- Drag elements - Use the toolbox to add classes, actors, activities, and more
- Connect components - Link elements with proper UML relationships
- Add details - Label relationships, multiplicities, and attributes
- Export - Save as PNG, SVG, or copy as image for documentation
Key Features
Drag-and-Drop Interface
Easy visual editing with drag-and-drop element placement.
Standard UML Notation
All diagrams follow official UML 2.x specifications and conventions.
Real-Time Preview
See your diagram update instantly as you make changes.
Auto-Layout
Automatic positioning of elements for clean, professional layouts.
Export Options
Download as PNG, SVG, or PDF for documentation and presentations.
Collaboration Ready
Share diagrams with team members for review and feedback.
Class Diagram Elements
Classes
- Name compartment
- Attribute section
- Method section
- Visibility modifiers (+, -, #)
Relationships
- Association (solid line)
- Aggregation (hollow diamond)
- Composition (filled diamond)
- Inheritance (hollow arrow)
- Dependency (dashed arrow)
Multiplicity
- 1 (exactly one)
- 0..1 (optional)
-
- (many)
- 1..* (one or more)
- n..m (range)
Sequence Diagram Elements
Lifelines
- Actor lifelines
- Object lifelines
- Activation boxes
Messages
- Synchronous messages
- Asynchronous messages
- Return messages
- Self messages
Control Flow
- Reframe boxes
- Alt/loop/opt fragments
- Activation periods
Use Case Diagram Elements
Actors
- Primary actors (user roles)
- Secondary actors (external systems)
Use Cases
- System functions
- Business processes
- User interactions
Relationships
- Include (dashed arrow)
- Extend (dashed arrow with stereotype)
- Generalization (hollow arrow)
Activity Diagram Elements
Actions
- Basic activities
- Call behavior actions
- Send signal actions
Control Flow
- Start node (filled circle)
- End node (filled circle in circle)
- Decision nodes (diamond)
- Fork nodes (thick bar)
- Join nodes (thick bar)
Partitions
- Swimlanes
- Responsibility areas
Why Use UML Diagrams?
Visual Communication
Communicate system design clearly to developers, stakeholders, and teams.
Documentation
Create visual documentation for system architecture and behavior.
Planning
Plan and structure code before implementation with visual models.
Analysis
Analyze system requirements and identify gaps in design.
Problem Solving
Visualize complex systems to identify issues and improvements.
Team Alignment
Ensure everyone understands the system design consistently.
Common Use Cases
Software Design
Model classes, relationships, and architecture for object-oriented systems.
System Analysis
Document functional requirements with use case diagrams.
Process Documentation
Visualize business processes with activity diagrams.
API Documentation
Document method calls and data flow with sequence diagrams.
Database Design
Model database schema and entity relationships.
Team Presentations
Create visual materials for design reviews and discussions.
Export Formats
| Format | Best For | Transparency |
|---|---|---|
| PNG | General use, presentations | Yes |
| SVG | Scalable graphics, web | Yes |
| Print documentation | No |
Technical Specifications
- UML Version - UML 2.x compliant
- Browser Support - All modern browsers
- Max Elements - Unlimited
- Export Resolution - Up to 4K
Frequently Asked Questions
Do I need UML experience?
No, our intuitive interface makes diagram creation accessible to everyone.
Can I save my diagrams?
Yes, save diagrams to your browser's local storage or export as files.
Can I import existing code?
Some diagram types support code import for automatic diagram generation.
Are the diagrams standard compliant?
Yes, all elements follow official UML 2.x specifications.
Can I collaborate with my team?
Share diagram links for review and collaborative editing.
Is the tool free?
Yes, all UML diagram features are completely free.
Browser Requirements
Works on all modern browsers including Chrome, Firefox, Edge, Safari, and Opera.
Related Tools: Flowchart Maker | Class Diagram Maker | Sequence Diagram Maker