Participants, Actors, and Lifelines
Declare each user, service, database, or external system before writing messages. Aliases keep the source concise while descriptive labels make each lifeline easy to identify.
PlantUML Sequence Diagram Online
Create a PlantUML sequence diagram online, model messages and conditions, preview the interaction, and export PNG or SVG.
PlantUML Sequence Diagram Online Editor
Start with the Sequence Diagram template, edit the PlantUML source, and preview the result live.
Use this focused sequence diagram tool for quick previews and exports. Open the full editor for AI generation, syntax repair, sharing, and saved projects.
Diagram preview
Create a PlantUML Sequence Diagram Online
Model participants, lifelines, requests, responses, conditions, loops, notes, and asynchronous messages in an editable PlantUML workspace with live preview and PNG or SVG export.
Built-in Sequence Diagram template
Start from valid PlantUML source designed for a practical sequence diagram.
Live diagram preview
See the rendered diagram update as you edit the PlantUML source.
Focused sequence diagram guidance
Learn the syntax and modeling choices used for API documentation, authentication flows, microservice calls, payment workflows, and architecture reviews.
PNG and SVG export
Download a shareable PNG or scalable SVG from the same source.
No local setup
Create and preview PlantUML without installing Java, Graphviz, or an IDE extension.
Continue in OnUML
Move to the full editor for AI generation, repair, sharing, and saved projects.
How to Create a PlantUML Sequence Diagram
Use the built-in template to create a sequence diagram for API documentation, authentication flows, microservice calls, payment workflows, and architecture reviews.
- 01
Start with the built-in Sequence Diagram template.
- 02
Rename the participants and arrange messages in time order.
- 03
Use alt, loop, opt, or par blocks for branches, repetition, and parallel work.
- 04
Preview the interaction and check that requests and responses are clear.
- 05
Export the finished sequence diagram as PNG or SVG.
PlantUML Sequence Diagram Syntax and Use Cases
Learn the core syntax and modeling decisions behind a useful sequence diagram, then apply them directly in the online editor above.
Requests and Return Messages
Use -> for a request and --> for a return value. Label arrows with meaningful actions or results so readers can understand the interaction without relying on surrounding documentation.
Client -> API: POST /login
API --> Client: 200 OK + access tokenConditions, Loops, and Parallel Work
Use alt and else for exclusive outcomes, loop for retries or batches, and par for independent work. These blocks keep realistic control flow inside one readable interaction timeline.
When to Use a Sequence Diagram
Use a sequence diagram when message order matters, such as an API call, login flow, payment, background job, or service orchestration. Use a class diagram instead when the static model is the main question.
PlantUML Sequence Diagram Example
The editable example demonstrates a practical sequence diagram. Change the source, check the live preview, and export the version you need.
@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
@endumlRelated PlantUML Tools
Use these related tools when you need a different export format or a full PlantUML editing workflow.
PlantUML Tools
Browse the complete OnUML matrix of online PlantUML tools and converters.
View all PlantUML toolsPlantUML Online Editor
Use the general editor when you want to switch freely between diagram types.
Open the general editorPlantUML Class Diagram Online
Create and export a focused class diagram with a built-in template.
Create a class diagramWhy Use PlantUML for Sequence Diagrams
PlantUML keeps sequence diagrams in reviewable text, making them easier to update, version, reuse, and export as the design changes.
Start from the right diagram type
Open directly into a Sequence Diagram template instead of adapting an unrelated example.
Keep the model reviewable
Store the diagram as readable text that works well in documentation and version control.
Preview before sharing
Check structure, labels, and relationships before exporting the rendered diagram.
Frequently Asked Questions
What is a PlantUML sequence diagram online tool?
It is a browser-based editor that starts with a Sequence Diagram template and lets you edit PlantUML source, preview the rendered diagram, and export PNG or SVG without local setup.
What can I model in a sequence diagram?
Use it to model participants, lifelines, requests, responses, conditions, loops, notes, and asynchronous messages. Common uses include API documentation, authentication flows, microservice calls, payment workflows, and architecture reviews.
How do I add an if/else branch to a PlantUML sequence diagram?
Wrap alternative outcomes in an alt block, add else for the second branch, and close the fragment with end.
Can PlantUML sequence diagrams show asynchronous messages?
Yes. Use ->> for an asynchronous message and combine it with par blocks when multiple interactions happen concurrently.
Can I export the sequence diagram as PNG or SVG?
Yes. Preview the diagram, then download PNG for slides and quick sharing or SVG for scalable documentation and web use.
Do I need to install PlantUML, Java, or Graphviz?
No. The online tool uses a server-backed preview, so you can edit and render the diagram directly in the browser.
Need AI-Assisted Diagram Editing?
Open the full OnUML editor for AI generation, syntax repair, sharing, saved projects, and multi-format diagram workflows.