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Using PlantUML

PlantUML is a tool for specifying various diagrams in a textual form. It is particularly useful in software projects where you want to update the diagrams incrementally, as the project evolves over time.

The sections below explains how to use PlantUML in a project.

Setting up PlantUML

This section explains how to install the PlantUML integration plugin in IntelliJ IDEA. If you are not using Intellij IDEA, you can refer to this guide on how to use PlantUML locally.

  1. Go to File > Settings to access the Settings page.

  2. Go to Settings > Plugins > Marketplace and install the plugin PlantUML integration.

  3. Then go to Settings > Languages & Frameworks > PlantUML or search for PlantUML. You can also use a specific version of PlantUML from the releases page. Settings - Other Settings - PlantUML: location of PlantUML.jar

Creating/editing/exporting diagrams

This section is for those using the PlantUML integration plugin in IntelliJ IDEA. Others can refer to this guide on how to use PlantUML locally.

After installing the PlantUML integration plugin, simply create or open any .puml file to start editing it.

Editing `DeleteSequenceDiagram.puml`

Any changes you make in editor pane on the left will be reflected in the preview pane on the right. However, do take note that these changes will not be reflected in your actual documentation until you export the diagram.

Saving the Diagram as an image

  • When using MarkBind as the site generation tool:
    • MarkBind has built-in support for PlantUML. The diagram will be generated and saved as an image automatically. No additional work needed from you.
  • When using Jekyll as the site generation tool:
    • The PlantUML integration plugin allows you to export individual diagrams to a location of your choosing. Click the Save Current Diagram Only button and choose the location to export the image file.
    • You will have to git add any new diagrams generated!

Tips and tricks

Maintaining consistency in formatting

It is highly recommended to consistently color your UML diagrams as an visual aid. You can achieve this by creating a dictionary of colors and import it like CSS.

For example, you can create a Style.puml with the contents:


!define LOGIC_COLOR #3333C4
!define LOGIC_COLOR_T1 #7777DB
!define LOGIC_COLOR_T2 #5252CE
!define LOGIC_COLOR_T3 #1616B0
!define LOGIC_COLOR_T4 #101086

Then you can use it in another PlantUML file like this:


!include Style.puml

box Logic LOGIC_COLOR_T2
participant ":LogicManager" as LogicManager LOGIC_COLOR
participant ":AddressBookParser" as AddressBookParser LOGIC_COLOR
participant ":UndoCommand" as UndoCommand LOGIC_COLOR
end box

You can fine-tune the formatting of PlantUML diagrams with the skinparam command. For example, skinparam backgroundColor transparent turns the background of the diagram transparent.

For a comprehensive list of skinparams, see unofficial PlantUML skinparam documentation.

Repositioning elements

While PlantUML’s automatic layout engine usually produces satisfactory results, at times the result can be less than ideal, especially on larger diagrams. Here is an example where the default layout generated by PlantUML has a lot of overlapping lines that are hard to decipher:

The UI class diagram without additional formatting

In most cases, you should consider decomposing the diagram into smaller ones or focusing on a more specific portion of the diagram.

Here are some techniques you can use to obtain a more palatable diagram.

By default, a short link (->) points to right and a long link (-->) points downwards. you can extend any link to make it longer (--->).

Length of arrows and its effects

Clever usage of arrow directions will resolve most layout issues. For example, the table below shows how the way in which you specify arrows can results in drastically different layouts for the same diagram.

Table: Link directions
Source Result
A --> Z
B --> Z
C --> Z
D --> Z

A --> 1 B --> 2 C --> 3 D --> 4

'default is down
A --> Z
'specify down
B -down-> Z
'shorthand for down
C -d-> Z
'arrow lengths take priority
D -down> Z

A -up-> 1
B -up-> 2
C -up-> 3
D -up-> 4
A -up-> Z
B -up-> Z
C -up-> Z
D -up-> Z

A --> 1
B --> 2
C --> 3
D --> 4

'Force A B C D
A -right[hidden]- B
B -right[hidden]- C
C -right[hidden]- D

Another technique you can use to influence the layout is to reorder definitions. The layout engine will attempt to order objects in the order in which they are defined. If there is no formal definition, the objects is taken to be declared upon its first usage.

Table: Definition ordering and outcomes
Source Result
A --> B
C --> D
'Class C is defined before A
Class C

A --> B
C --> D
package "Rule Of Thumb";{
    Class C
    A --> B
    C --> D

Explicitly define all symbols to avoid any potential layout mishaps.