DiagramPreview
Basic parserServer SVGText diagramsExport ready

PlantUML Preview

Paste PlantUML text and generate a shareable SVG preview through the PlantUML server URL format.

Examples
PlantUML previewReady
Your PlantUML preview will appear here.

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How to use

  1. 1Paste a complete PlantUML document that includes @startuml and @enduml.
  2. 2Choose a sequence, class, use case, or activity sample when you need a known-good starting point.
  3. 3Review the rendered SVG for missing participants, unreadable labels, styling that hides meaning, and remote include dependencies.
  4. 4Reduce failing diagrams to a minimal source before adding skinparam, notes, sprites, or complex blocks back.
  5. 5Export the rendered result only after confirming the source can still live beside the documentation.

Common use cases

Sequence diagramsUML class sketchesUse case diagramsActivity flow reviewArchitecture decision recordsCode review documentation

Related tools

PlantUML to Draw.io

Convert PlantUML sequence, component, class, and activity diagrams into editable draw.io / diagrams.net XML.

Mermaid Preview

Preview Mermaid diagrams online with a live editor, syntax checks, examples, and SVG/PNG export.

AI PlantUML Generator

Generate PlantUML diagrams from natural language with DeepSeek.

FAQ

How does PlantUML rendering work?

The first release encodes the PlantUML source and displays the SVG generated by the PlantUML server.

Can the renderer be replaced later?

Yes. The PlantUML URL builder is isolated behind a renderer module.

What should I check before publishing a PlantUML diagram?

Confirm the source is complete, labels are short enough, remote includes are intentional, and the rendered SVG still matches the system or workflow being documented.

Is server-rendered PlantUML suitable for private diagrams?

Use a trusted private renderer for sensitive diagrams. Server rendering can send PlantUML source to the renderer that creates the SVG.

PlantUML Preview helps teams review UML-style diagrams without leaving the browser. It is useful for sequence flows, classes, activities, and use case diagrams that belong beside engineering documents.

The first version uses the standard PlantUML server URL approach. The encoding logic is isolated so a later local or private renderer can replace it without changing the page contract.

Because the editor uses plain text, diagrams can move cleanly between code review, wikis, issue trackers, and exported SVG assets.

Demo: document a login sequence with PlantUML

PlantUML is strong when a diagram needs to live beside code. A compact sequence source can explain authentication, token exchange, and failure handling without drawing by hand.

  • Name participants exactly as they appear in the system boundary.
  • Keep messages short enough for review comments and wiki pages.
  • Use alt blocks for expected failure paths instead of writing them only in prose.
@startuml
actor User
participant Web
participant Auth
database SessionDB
User -> Web: submit credentials
Web -> Auth: verify password
Auth -> SessionDB: create session
Auth --> Web: token
Web --> User: signed in
@enduml

Troubleshooting: isolate server-rendered PlantUML failures

When PlantUML rendering fails, the fastest path is to reduce the source until the server accepts it, then add styling, notes, and complex blocks back gradually.

  • First test @startuml and @enduml with two nodes only.
  • Check whether remote includes, sprites, or skinparam blocks depend on unavailable resources.
  • Keep private diagrams on trusted renderers because server rendering can send source to that renderer.
@startuml
Alice -> Bob: ping
Bob --> Alice: pong
@enduml

Review pattern: keep PlantUML source maintainable

PlantUML diagrams work best when the text source remains readable in code review. Heavy styling, large includes, and dense diagrams can make the rendered image look polished while the source becomes hard to maintain.

  • Keep participant and class names close to the terminology used in code or docs.
  • Use notes for assumptions instead of hiding them in long message labels.
  • Split unrelated class, sequence, and activity views into separate diagrams.
@startuml
participant Client
participant API
note over API: Validate token before reading orders
Client -> API: GET /orders
API --> Client: 200 OK
@enduml

Review checklist for PlantUML Preview

Use PlantUML Preview when you need to inspect source content visually before it becomes documentation, a pull request note, an incident write-up, or a handoff artifact. Preview PlantUML diagrams from text using a replaceable server renderer.

Before exporting, check that labels are readable, relationships match the source, generated examples do not contain private data, and the preview still makes sense after you edit the input.

Limits and troubleshooting

If the preview fails, reduce the input to the smallest complete example, confirm the format syntax, and then add sections back one at a time. Many rendering failures come from partial files, indentation mistakes, missing diagram headers, or copied snippets that depend on hidden context.

Treat the preview as a review surface rather than a source of truth. Generated diagrams, converted files, dashboards, and rule examples should be checked before they are used in production documentation or operations.

Example inputs to test

  • Sequence: @startuml actor User participant App participant Service User -> App: Submit diagram App -> Service: Render Service --> App: SVG App --> User: Preview @enduml
  • Class: @startuml class Diagram { +source: string +render(): SVG } class PlantUMLDiagram Diagram <|-- PlantUMLDiagram @enduml
  • Use case: @startuml left to right direction actor Developer rectangle DiagramPreview { Developer -- (Preview PlantUML) Developer -- (Export SVG) } @enduml

Tool maturity

Basic parser

Basic parser

This tool focuses on fast structure inspection. Use it for review and debugging, then verify critical output before production use.

The maturity label is not a quality score. It tells visitors whether the tool is best for stable export, deeper debugging, quick parsing, or AI-assisted generation.