UML State Diagrams with PlantUML

2020-02-0817:25 CET

For refactoring the state machine in waschbot, I wanted to draw a state diagram. I wanted some program that would transform a textual representation of the diagram into an image file, eg. png.

The first tool I found was mermaid.js, but a) it’s JavaScript and you need node, npm, yarn and a metric crapton of 46 dependencies and b) the command-line tool (mermaid.cli) has seen no commits for 2 years and c) the examples wouldn’t compile. The demo web-editor was okay, though.

After some more googling, I found PlantUML and it’s pretty much what I wanted.

Install the tool:

$ brew install plantuml

Write an example.uml:

@startuml
	[*] -right-> tanz: start
	tanz -down-> [*]: stop
	tanz -right-> rüttel
	rüttel -up-> schüttel
	schüttel -left-> wirf
	wirf -down-> tanz
@enduml

Compile the example:

$ plantuml example.uml

The resulting png file:

Es tanzt ein Bi-Ba-Butzemann in unserm Haus herum!

PlantUML supports theming to make the output less ugly, skinparam monochrome true seems to be a good starting point. Compiling takes a little too long for my taste, apart from that I’m happy.