Free UML Diagram Tool Online
Create UML diagrams in your browser with live PlantUML preview and PNG or SVG export. Pick a focused maker for the diagram type you need, or open the studio for a blank canvas.
What is a UML diagram?
A UML diagram is a standard visual for modeling software structure and behavior. UML stands for Unified Modeling Language. Teams use these diagrams to agree on design, document services for onboarding, and explain flows to people who will not read every source file.
Structural diagrams describe what exists: classes, objects, components, packages, and deployment nodes. Behavioral diagrams describe what happens: message sequences, activities, use cases, and state changes. Choosing the right view answers a specific question instead of forcing every detail onto one crowded picture.
Features
- Live PlantUML preview
- No install required
- PNG and SVG export
- Starter templates for common diagrams
- Free to use in the browser
Diagram tools by category
Each tool page includes a live editor, a starter template, and a short guide for that diagram type.
Structural UML
Show what the system is made of: classes, objects, components, packages, and deployment.
- Class Diagram MakerBuild a UML class diagram in your browser. Start from the template, rename types to match your domain, and exp…
- Object Diagram MakerDraw an object diagram when you need a snapshot of instances, not just types. Start from the template, fill in…
- Component Diagram MakerShow how larger software pieces depend on each other. Start from the template, rename components to match your…
- Package Diagram MakerMap packages and dependency direction so illegal imports show up early. Adapt the layered starter to your modu…
- Deployment Diagram MakerDocument where software runs: hosts, containers, artifacts, and communication paths. Rename the starter nodes …
- Composite Structure Diagram MakerModel the inside of a complex class or component when a black-box view is not enough. Adapt the starter parts …
- Profile Diagram MakerCreate a UML profile when your team needs shared stereotypes and tagged values beyond stock UML. Start from th…
Behavioral UML
Show what happens over time: interactions, workflows, use cases, and state changes.
- Sequence Diagram MakerDraw a sequence diagram for auth flows, service calls, and feature interactions. Start from the template, keep…
- API Sequence Diagram MakerDocument an API call path with a sequence diagram: client, gateway, services, and status codes that matter. Ad…
- Activity Diagram MakerMap a workflow with actions, decisions, and end states. Start from the template, rename steps to match your pr…
- Use Case Diagram MakerShow who uses the system and which goals they pursue. Start from the template, keep use cases at goal level, a…
- State Diagram MakerModel a lifecycle with states and transitions. Ideal for order status, document review, and device modes. Adap…
- Communication Diagram MakerUse a communication diagram when structural links matter as much as message order. Start from the template, nu…
- Timing Diagram MakerPlot state or condition against time when duration and overlap matter more than a simple message list. Adjust …
- Interaction Overview Diagram MakerSketch a map of several interactions when one sequence diagram would be too dense. Adapt the starter flows, th…
PlantUML Editor
Write PlantUML in the browser with live preview and export.
Code-focused
Class diagrams tuned for Java and Python codebases.
Related diagrams
ERD, flowchart, DFD, swimlane, C4, and microservices views teams use beside UML.
- ER Diagram MakerDesign an entity-relationship diagram for tables, keys, and cardinalities. Start from the template for schema …
- Flowchart MakerCreate a flowchart for processes, support scripts, and simple algorithms. Start from the template, keep labels…
- Data Flow Diagram MakerBuild a data flow diagram to show how data moves between processes, stores, and external entities. Adapt the s…
- Swimlane Diagram MakerSeparate process steps into lanes by role or system so ownership stays visible. Start from the template, renam…
- C4 Diagram MakerDraft C4-style context and container views for architecture talks. Start from the template, keep one level of …
- Microservices Diagram MakerMap services, gateways, and datastores so ownership and call paths stay visible before the mesh grows. Adapt t…
How to create a UML diagram here
- Open the maker that matches your question (structure, behavior, data, or architecture).
- Edit the starter so names match your domain.
- Check the live preview.
- Export PNG or SVG for docs, tickets, or slides.
Prefer a blank canvas? Use the studio or the PlantUML online editor.
Popular starting points
Class diagrams
Types, fields, methods, and relationships for object-oriented design.
Sequence diagrams
Message order between actors and services for feature and API flows.
Activity diagrams
Workflows, decisions, and business or product procedures.
Use case diagrams
Actors and goals at the system boundary for requirements workshops.
ER diagrams
Entities, keys, and relationships for database design.
PlantUML online
Text-based diagrams you can keep next to code reviews.
Why text-based diagrams
Text diagrams review cleanly in pull requests and stay versionable in git. This site keeps that workflow in the browser so everyday drafting does not require a local Java install. Drag-and-drop tools are still useful in workshops. Use whichever medium your audience will actually read.
Frequently asked questions
What is a UML diagram?
A standardized visual for modeling software structure and behavior using Unified Modeling Language notation.
Is this UML diagram tool free?
Yes. You can create and export diagrams online without a paid subscription.
What can I create here?
Class, sequence, activity, use case, state, component, deployment, ER, flowchart, DFD, C4-style architecture, and more through the tools directory.
Do I need to install anything?
No. Editors run in the browser with live preview and export.
Ready to make a diagram?
Start with a focused maker or open the full studio. No signup required.