PlantUML — Generate UML Diagrams from Plain Text

Introduction

PlantUML is an open-source tool that renders diagrams from a concise text-based syntax. Instead of dragging shapes in a GUI, developers write markup that PlantUML compiles into images, making diagrams versionable, diffable, and embeddable in documentation pipelines.

What PlantUML Does

• Generates sequence, class, activity, component, state, and object diagrams from text
• Supports non-UML diagrams including Gantt charts, mind maps, JSON/YAML visualization, and wireframes
• Renders output in PNG, SVG, EPS, and LaTeX formats
• Integrates with wikis, Markdown processors, IDEs, and CI pipelines via plugins
• Runs as a standalone JAR, a Docker container, or through the public rendering server

Architecture Overview

PlantUML is a Java application that parses its custom DSL into an internal model, then lays out elements using Graphviz (dot) for graph-based diagrams or its own layout engine for sequence and activity diagrams. The parser handles includes, preprocessor macros, and themes. Output rendering delegates to standard Java2D for raster and SVG writers for vector formats.

Self-Hosting & Configuration

• Requires Java 8+ and optionally Graphviz for class and component diagrams
• Install via package managers: brew install plantuml or apt install plantuml
• Run as a Docker container: docker run -p 8080:8080 plantuml/plantuml-server
• Embed in CI with a simple plantuml *.puml step to generate images from source
• Configure themes and includes via !theme directives or a shared plantuml.cfg file

Key Features

• Text-based source files that version cleanly in Git alongside code
• Over 20 diagram types covering UML, architecture, and project management
• Preprocessor with variables, includes, and conditional blocks for reusable templates
• Extensive theming system with built-in and custom color schemes
• Editor plugins for VS Code, IntelliJ, Eclipse, and Emacs with live preview

Comparison with Similar Tools

• Mermaid — JavaScript-based with Markdown integration; PlantUML has more diagram types and richer layout
• draw.io — GUI-based drag-and-drop editor; PlantUML is text-first and diff-friendly
• Structurizr — focuses on C4 architecture models; PlantUML covers broader UML and non-UML types
• Kroki — aggregator service that renders PlantUML and others; PlantUML is the underlying engine
• Lucidchart — SaaS diagramming platform; PlantUML is free, offline, and developer-oriented

FAQ

Q: Do I need Graphviz installed? A: For sequence and activity diagrams, no. For class, component, and deployment diagrams, Graphviz is required for layout.

Q: Can I use PlantUML in Markdown documentation? A: Yes. Tools like MkDocs, Docusaurus, and GitLab natively support PlantUML code blocks or via plugins.

Q: Is there a public rendering server? A: Yes. The official server at plantuml.com renders diagrams without local installation, but a self-hosted server is recommended for private content.

Q: What output formats are available? A: PNG, SVG, EPS, PDF, and LaTeX/TikZ.

Sources

• https://github.com/plantuml/plantuml
• https://plantuml.com