Mermaid vs PlantUML

Updated October 2026 · AppBreakup editorial

Mermaid

Open-source JavaScript library that turns Markdown-like text into diagrams.

Open sourceSelf-hostable

Visit Mermaid Mermaid profile

PlantUML

Open-source tool that draws UML and other diagrams from plain-text descriptions.

Open sourceSelf-hostable

Visit PlantUML PlantUML profile

The short answer

Pick Mermaid if you want simple text diagrams that render directly in GitHub, GitLab, Notion, Obsidian and similar tools with no setup. Pick PlantUML if you need the broadest UML coverage, such as detailed sequence, component and deployment diagrams, and are happy to run a renderer. Both are free diagrams-as-code tools; the biggest difference is native rendering in popular tools against breadth of diagram types.

Mermaid or PlantUML: our take

Both let you write a diagram as text and render it as an image, so diagrams can be versioned in Git, reviewed in pull requests and kept beside the code they describe. Mermaid uses a short, Markdown-inspired syntax and covers flowcharts, sequence, class, state and entity-relationship diagrams, Gantt charts, user journeys, Git graphs and mind maps. PlantUML is one of the oldest diagrams-as-code tools. You write between @startuml and @enduml, and it produces sequence, class, use case, activity, component, state and deployment diagrams, plus Gantt charts, mind maps, wireframes, network diagrams and JSON or YAML visualisations. Its UML coverage is broader than Mermaid's.

Both are free and open source. Mermaid is MIT licensed, with an online Mermaid Live Editor; its creators also run Mermaid Chart, a separate commercial editor. PlantUML is offered under several licences, LGPL-3.0 in its repository and a GPL build that is the most complete.

Setup is where they differ in practice. Mermaid renders in the browser and is supported natively by GitHub, GitLab, Notion, Obsidian and Confluence apps, so a diagram in a README or note simply appears. PlantUML runs as a Java program, through a public online server or via plugins for VS Code, IntelliJ, Confluence and many documentation tools, and a JavaScript renderer now works in the browser too. Running it locally means installing Java and sometimes Graphviz, though you can self-host a rendering server.

Both share the same weakness: automatic layout gives little control, and big diagrams get hard to read. PlantUML's default style looks dated and its syntax varies between diagram types; Mermaid's styling options are limited. For documentation in Markdown and repositories, Mermaid is usually the easier choice. For teams doing detailed UML or software architecture work inside an IDE or Confluence, PlantUML offers more.

Choose Mermaid if…

Developers who want diagrams as text that render in GitHub, docs and wikis
Diagrams are plain text you can version and review
Rendered natively by GitHub, GitLab and many doc tools

Choose PlantUML if…

Engineers documenting software with UML diagrams kept as text in the repo
You need Windows, macOS and Linux, which Mermaid doesn't list
Very broad UML coverage
Plugins for most IDEs and documentation tools

What is Mermaid?

Mermaid lets you describe a diagram in a short text syntax and renders it as an image in the browser. It supports flowcharts, sequence, class, state and entity-relationship diagrams, Gantt charts, user journeys, Git graphs, mind maps and more. Because diagrams are plain text, they can be versioned in Git, reviewed in pull requests and kept next to the code they describe, and many tools render Mermaid natively, including GitHub, GitLab, Notion, Obsidian and Confluence apps. The project is MIT licensed and free; you can try it in the online Mermaid Live Editor. Its creators also run Mermaid Chart, a separate commercial editor with visual editing, AI and team features. The trade-off is control: automatic layout decides where boxes go, so large or carefully arranged diagrams can be hard to get looking right, and styling options are limited compared with a drawing tool.

What is PlantUML?

PlantUML is one of the oldest diagrams-as-code tools. You write a description between @startuml and @enduml and it produces sequence, class, use case, activity, component, state and deployment diagrams, plus non-UML formats such as Gantt charts, mind maps, wireframes, network diagrams, JSON and YAML visualisations. It runs as a Java program, through a public online server, or via plugins for VS Code, IntelliJ, Confluence, Markdown tools and many documentation systems, and an in-browser JavaScript renderer is now available too. The project is open source and offered under several licences, with the GPL build the most complete. Its UML coverage is broader than Mermaid's and its long history means most questions have an answer somewhere, but the default look is plain, the syntax has many quirks, and running it locally means installing Java and sometimes Graphviz.

Side by side

Attribute	Mermaid	PlantUML
Pricing	Open source	Open source
Open source	Yes	Yes
Self-hostable	Yes	Yes
Platforms	Web, Self-hosted	Web, Windows, macOS, Linux, Self-hosted
Best for	Developers who want diagrams as text that render in GitHub, docs and wikis	Engineers documenting software with UML diagrams kept as text in the repo
Status	Active	Active

Verified facts, compared

Facts both apps publish, checked on each vendor's own site.

Fact	Mermaid	PlantUML
License	MIT	LGPL-3.0 (repo); GPL and other builds offered