PlantUML

What PlantUML is

PlantUML is an open source component that creates diagrams from simple textual descriptions. You write a few lines such as Car --|> Vehicle and ParkingLot *-- Level, and PlantUML draws the class diagram. Change the text, and the picture updates.

Which diagrams it supports

The project lists these UML diagrams: sequence, use case, class, object, activity, component, deployment, state and timing diagrams. It also draws many non-UML diagrams, including JSON and YAML data, EBNF grammars, regular expressions, network diagrams, wireframes, ArchiMate, Gantt charts, mind maps, work breakdown structures and entity relationship diagrams.

For a software design roadmap you need four of them: class, sequence, state and use case diagrams.

Why diagrams as text

• Version control: diagrams live in Git next to the code they describe, so you can see how a design changed over time.
• Review: a design change shows up as a readable diff in a pull request.
• Speed: once you know the syntax, writing a diagram is faster than dragging boxes, and the layout is automatic.
• No lock-in: the source is plain text that any editor can open.

The trade-off is layout control. Automatic layout is good for small and medium diagrams, but for a large or carefully arranged diagram a drawing tool can look better.

How to start

The official site documents each diagram type with examples, starting with the class diagram page. You can render diagrams in a browser, from the command line, or through plugins and integrations. The project also publishes a browser extension that renders PlantUML directly inside GitHub, and an MCP server so AI assistants can render and check diagrams.

PlantUML or Mermaid?

Both turn text into diagrams. Mermaid renders natively in GitHub Markdown and many documentation tools, which makes it the easiest choice for a README. PlantUML covers more UML diagram types and more notation detail. Many developers use Mermaid for quick README diagrams and PlantUML for fuller design documents.

Common questions

Is it free? Yes, PlantUML is open source.

Do I need to know all of UML? No. Learn class boxes, the five relationship arrows, multiplicity and sequence diagrams, and you can draw nearly every design you will discuss.

Best for: students and engineers who want diagrams that stay next to the code and get reviewed like code.