PlantUML vs Mermaid: Which Diagram Tool Should You Use?
Both turn plain text into diagrams, and both are free. They differ in which diagrams they draw well, where they render without extra setup, and where your diagram source goes. Here is how to choose.
PlantUML vs Mermaid is the usual choice for anyone who wants diagrams as code: text in the repository, reviewed like code, rendered into an image. The PlantUML Editor writes and previews PlantUML in the browser. This guide compares the two tools so you can pick one per project and stick with it.
PlantUML vs Mermaid syntax side by side
The same sequence diagram, an order request passing through an API to a database, in each language:
@startuml
actor User
User -> API: POST /orders
API -> DB: insert order
DB --> API: id
API --> User: 201 Created
@endumlsequenceDiagram
actor User
User->>API: POST /orders
API->>DB: insert order
DB-->>API: id
API-->>User: 201 CreatedFor simple diagrams the two are close, and moving between them is quick. The differences show up in the diagram types, the layout control and where the diagrams render.
Diagram types each tool draws well
- PlantUML covers the full set of UML diagrams: sequence, use case, class, object, activity, component, deployment, state and timing. It also draws Gantt charts, mind maps, work breakdown structures and visualisations of JSON and YAML data. Its
skinparamsettings give detailed control over layout and style. - Mermaid focuses on the diagrams most common in documentation: flowcharts, sequence, class, state and entity relationship diagrams, plus Gantt charts, pie charts, git graphs, mind maps and timelines. Styling options are simpler.
If your team draws component and deployment diagrams for architecture documents, PlantUML has the more complete notation. For flowcharts and quick sequence diagrams in a README, Mermaid is enough. See the PlantUML sequence diagram guide for the full PlantUML sequence syntax.
Where each renders without extra setup
- GitHub renders Mermaid code blocks in Markdown files, issues and pull requests. It does not render PlantUML; commit an exported SVG instead.
- GitLab renders Mermaid out of the box, and renders PlantUML when the instance administrator enables its PlantUML integration.
- Confluence renders neither on its own. Teams use a marketplace app, or embed a diagram from an external tool. The PlantUML Editor here can produce an embed link for this purpose.
Where your diagram source goes
Mermaid renders in the browser with JavaScript, so a diagram never has to leave the page. PlantUML was traditionally rendered by a Java program, and many online editors and plugins send the diagram source to a PlantUML server to draw it. For architecture diagrams that show internal systems, check where your tool renders. The PlantUML Editor renders in your browser, so the source is not sent to a rendering server.
PlantUML or Mermaid: how to choose
- Choose Mermaid when diagrams live in GitHub or GitLab Markdown and are mostly flowcharts and simple sequences.
- Choose PlantUML for detailed UML, large architecture diagrams, or when you need fine control over layout.
- Pick one per repository. Two diagram languages in one project means two syntaxes for reviewers to learn and two ways of rendering to maintain.
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