PLANTUML is a popular open-source tool for creating UML (Unified Modeling Language) diagrams. It uses simple and intuitive text language to describe diagrams. The files with .plantuml file extensions are the text files containing the descriptions of diagrams in the textual language used by PlantUML. These files can be processed by PlantUML to generate UML diagrams.

Using the PlantUML Online Server

One of the most straightforward ways to open and use files with the PLANTUML extension is through the PlantUML Online Server. All you need to do is open the PlantUML Online Server in your web browser, paste your code into the text box provided in the middle of the homepage, and then click 'Submit'. This will instantly crash your UML diagram.

Installing the PlantUML Tool Locally

If you would like to work offline or if you have a large number of PLANTUML files, installing the PlantUML tool on your local machine may be a better option. You can download the tool from the official PlantUML download page. Once it's installed, you can open your PLANTUML files with any text editor, and then use the command line to process the files and generate diagrams.

Using Integrated Development Environments (IDEs)

Several popular Integrated Development Environments (IDEs) provide built-in support or plug-ins for PlantUML. These IDEs include IntelliJ IDEA, Visual Studio Code, and Eclipse. Once you have installed the PlantUML plug-in into your IDE, you can open your PLANTUML files directly in the IDE and preview or generate the diagrams without needing to use the command line. For instance, if using Visual Studio Code, you can download the PlantUML extension from the Visual Studio Code Marketplace.

PLANTUML File Important Information

While the PLANTUML file extension allows for easy and visually appealing documentation of software and system designs, users need to be aware of certain critical information regarding its use. For starters, since the PLANTUML language is sensitive to errors, careful attention must be given to syntax while creating or modifying these files. Also, as the UML diagrams generated are images, text inside the diagrams may not be as accessible or searchable as in other forms of documentation. This is an important consideration for people planning to use PlantUML for large projects requiring easy text search and access.