Eclipse Layout Kernel

PlantUML uses an external layout engine for some diagrams (classes, use cases...). By default, GraphViz/dot is used. This means that PlantUML has to call an external process to generate some diagrams.

There are some work in progress to change this behavior. For example, a port of GraphViz to Java is ongoing.

Recently, Hallvard Trætteberg teaches us on how to use Eclipse Layout Kernel as a library to process the layout.

This is still alpha-software, but results are very interesting. This is working starting from V1.2021.5.


ELK is distributed as an independent library. So you have to build it yourself, or you can download the complete jar file here.

Both plantuml.jar and elk-full.jar have to be in the very same folder. You cannot rename elk-full.jar

Once installed, you can invoke ELK instead of GraphViz with the !pragma layout elk directive.


!pragma layout elk

package image {
	package color {
		class red
		class green
		red->green : red to green
	package size {
		class big
		class small
	class image1
	class image2
	image1 <|-- image2 
	size -> color : link between packages

class foo
class bar

foo -> bar : foo to bar
image1 "1" -> "*" bar

This diagram is generated using ELK.

Do not expect too much right now, this is really an alpha-version. The idea is to get feedback from users, to know if we should continue in this direction (that is, supporting ELK within PlantUML).

Still, you can test class diagram and deployment diagram and tell us what you think about the result.

Thanks for your attention !