PlantUML online tool
PlantUML Online Editor
Edit PlantUML code online, preview diagrams instantly, and open the full OnUML editor when you need AI generation, syntax repair, or sharing.
Simple PlantUML Editor
Edit the sample and preview the rendered diagram instantly.
This lightweight editor is for quick preview. Use the full editor for AI generation, AI syntax repair, sharing, and project workflows.
Features for PlantUML Online Editing
Use this page for quick PlantUML previews, then continue in OnUML when your diagram needs AI assistance or a shareable editing workflow.
Live diagram preview
Render PlantUML code in the browser without installing local tooling.
Edit PlantUML online
Use the lightweight editor for quick syntax checks and diagram previews.
Continue in OnUML
Open the full editor when you need AI generation, repair, and sharing.
No local setup
Try PlantUML without installing Java, Graphviz, or an IDE extension.
AI help in the full editor
Generate PlantUML from prompts and repair syntax issues in the complete OnUML editor.
Online preview workflow
Check PlantUML output in the browser before moving into a larger diagram workflow.
How to Use the PlantUML Online Editor
The simplified editor is designed for quick PlantUML checks. For complete diagram workflows, continue in the OnUML editor.
- 1
Edit the PlantUML code in the sample editor.
- 2
Check the rendered diagram preview.
- 3
Reset the example when you want to start over.
- 4
Open the full editor for AI help, sharing, and project workflows.
PlantUML Example
PlantUML uses text to describe diagrams. The example below defines a simple sequence diagram with a user, the OnUML editor, and a PlantUML server.
@startuml
actor User
participant "OnUML Editor" as Editor
participant "PlantUML Server" as Server
User -> Editor: Write PlantUML code
Editor -> Server: Render diagram preview
Server --> Editor: Return diagram
Editor --> User: Show live preview
@endumlWhy Use OnUML for PlantUML
OnUML is more than a PlantUML viewer. It gives you a path from quick preview to AI-assisted diagram creation across PlantUML, Mermaid, and draw.io.
Start with a fast online check
Use the lightweight PlantUML editor to test syntax, adjust the diagram text, and confirm the result before moving into a larger workflow.
Move from draft to assisted editing
When the diagram needs more work, continue in OnUML to generate new PlantUML, repair syntax issues, and refine structure with AI help.
Keep diagram work in one place
OnUML supports PlantUML alongside Mermaid and draw.io, so teams can review and maintain different diagram formats in a single workspace.
Frequently Asked Questions
What is a PlantUML online editor?
A PlantUML online editor lets you write PlantUML code in the browser and preview the rendered diagram without installing Java, Graphviz, or an IDE extension.
Is this PlantUML editor free to try?
Yes. You can edit the sample PlantUML code and preview the diagram directly on this page. The full OnUML editor also includes a free workflow for creating and editing diagrams.
Can I use this page as a PlantUML viewer?
Yes. Paste or edit PlantUML code in the online editor and use the preview panel to check how the diagram renders.
Do I need to install Java or Graphviz?
No. This online page renders PlantUML through a server-backed preview, so you do not need to install Java, Graphviz, or a local PlantUML extension.
Can OnUML fix PlantUML syntax errors?
Yes. Syntax repair is available in the full OnUML editor. This page shows a quick preview and directs you to the complete editor when you need AI repair.
What is the difference between this page and the full editor?
This page is a fast PlantUML preview tool for trying code. The full editor adds AI generation, AI repair, sharing, project workflows, and support for Mermaid and draw.io.
Continue in the Full OnUML Editor
Use AI generation, AI repair, sharing, and multi-format diagram editing in the complete OnUML workspace.
Start Editing PlantUML