Comparison · October 2026
PlantUML vs Mermaid Online
PlantUML and Mermaid both turn plain text into diagrams, and both are free — so the real difference is everything around the syntax. PlantUML is the veteran: wide formal UML coverage and deep integrations into doc pipelines, in exchange for a Java runtime or a render server and hand-tuned skinparam styling. Mermaid Online renders in any browser with zero setup, designed export themes, and an AI assist. Here is how the two stack up, fact by fact.
Zero install · No Java · No server · No watermark · Local browser rendering
Side by side
as of October 2026 · verified against PlantUML's public pricing and product pages
| Feature | Mermaid Online | PlantUML |
|---|---|---|
| Setup | Open a URL and paste code — nothing to install | Java runtime (plus Graphviz for many diagram types) locally, or a render server |
| Where code is processed | Locally in your browser | On the public or self-hosted PlantUML server, or locally with Java |
| Diagram coverage | Flowchart, sequence, class, state, ER, Gantt, pie, mindmap, timeline, git graph | Wider formal UML 2.x set — use case, activity, component, deployment, object, timing — plus ArchiMate, WBS, network, JSON/YAML |
| Styling | 9 designed export presets, dark and transparent variants, live preview | skinparam directives — powerful but low-level, no designed themes |
| Watermark on free exports | None | None — the tool is open source |
| Export formats | PNG, SVG, JPG, WebP, PDF at 1x–4x, straight from the browser | PNG, SVG, EPS, PDF and more via the server or command line |
| AI diagram generation | Text or screenshot to Mermaid, free credits to start | — |
| Cloud diagram library | 3 saved diagrams free, unlimited on Pro | — |
| Doc-tool integrations | Mermaid renders natively on GitHub, GitLab, and Notion; images paste anywhere | Deep plugin ecosystem: IDE plugins, Confluence/Jira/Word macros, Sphinx, AsciiDoc, Doxygen, mkdocs |
| Paid plan | Pro $5.99/mo for AI credits, premium themes, and the cloud library | No paid plan — free and open source; the server is self-managed |
PlantUML is a free, open-source (GPL) text-to-diagram tool first released in 2009, widely used in software documentation and doc-tool pipelines. This page states verifiable public facts only; check both tools before you decide.
Try a no-watermark export
The fastest check is your own diagram: paste the code below, export PNG or SVG at up to 4x, and compare the output with what your current tool gives you. Everything renders locally in your browser.
Export controls activate after your diagram renders locally.
FAQ
Questions about this comparison
Is PlantUML free?+
Yes. PlantUML is free and open source under the GPL, and the public render server at plantuml.com is free to use. Teams that cannot send diagram code to a public server run their own server or the local jar.
Do I need Java to use PlantUML?+
For local rendering, yes — the standard setup is a Java runtime plus Graphviz. The online demo server avoids local Java, but it processes your diagram text on that server, which matters for confidential diagrams. Mermaid Online has no such trade-off: rendering happens in your browser with nothing installed.
Which tool supports more diagram types, Mermaid or PlantUML?+
PlantUML. Its formal UML 2.x coverage is wider — use case, component, deployment, object, and timing diagrams — and it adds ArchiMate, WBS, and network diagrams. Mermaid covers the set most docs and READMEs need: flowchart, sequence, class, state, ER, Gantt, pie, mindmap, timeline, and git graph.
Can PlantUML diagrams look styled?+
Yes, through skinparam directives, which control colors, fonts, and borders line by line. It is full control but hand-tuned work. Mermaid Online ships nine designed export presets — including dark and transparent variants — that are one click away.
Should I pick Mermaid or PlantUML?+
If you are documenting formal UML models or wiring diagrams into Sphinx, AsciiDoc, or Confluence pipelines, PlantUML is the stronger fit. If you want to paste text into a browser and download a clean, styled image in seconds — with zero install — Mermaid Online is the faster path. Many teams use both.
Is Mermaid Online affiliated with PlantUML or Mermaid.js?+
No. Mermaid Online is an independent tool and is not affiliated with PlantUML, Mermaid.js, or their maintainers.