Mermaid vs PlantUML vs Graphviz
Three text-to-diagram tools, three different jobs. Mermaid is concise and renders in the browser; PlantUML is the deepest for UML; Graphviz lays out big graphs. Here is how they actually differ.
⚠️ Disclosure: we build a free Mermaid editor. The criteria below — syntax, diagram types, how each renders, GitHub support — are objective; verify any of them against each project’s own docs.
| Tool | Syntax style | Diagram types | How it renders | GitHub native | Best for |
|---|---|---|---|---|---|
| Mermaid | Concise, Markdown-like | Flowchart, sequence, ER, class, state, Gantt, mind map, pie, more | JavaScript — renders in the browser | Yes — native in Markdown | Docs-as-code in READMEs, wikis and notes |
| PlantUML | Verbose DSL (@startuml … @enduml) | The most complete UML set, plus many non-UML diagrams | Java — a PlantUML server or local jar | No — needs a pre-rendered image | Deep, exhaustive UML modelling |
| Graphviz (DOT) | Graph description language (digraph { … }) | General node-and-edge graphs, trees, dependency maps | Graphviz engine (dot); WASM ports for the browser | No — needs a pre-rendered image | Large auto-laid-out graphs and hierarchies |
“GitHub native” means the diagram renders from source in Markdown with no image upload. PlantUML and Graphviz need a pre-rendered SVG/PNG to appear on GitHub.
When to pick each one
Choose Mermaid when the diagram documents code and should live in the repo — a README architecture sketch, a sequence diagram in a design doc, a schema in a wiki. It renders natively on GitHub and GitLab, so reviewers see it inline, and the syntax is light enough to write in the flow of typing notes.
Choose PlantUML when you need rigorous, complete UML — detailed class hierarchies, component and deployment diagrams, or precise control over notation. You trade the native GitHub rendering and brevity for depth, and you run a PlantUML server (or the jar) to produce images.
Choose Graphviz when the “diagram” is really a large graph whose layout you do not want to place by hand — dependency graphs, call graphs, big state machines. Its DOT language plus automatic layout engine handle hundreds of nodes that would be unmanageable to draw manually.
If you landed here to make a diagram now, the fastest path is Mermaid: open the editor, try the UML class diagram generator, or browse examples you can copy. To put one in a repo, see how to embed Mermaid.
Frequently asked questions
Mermaid vs PlantUML — which is better?
Neither is strictly better; they target different jobs. Mermaid is concise and renders natively in Markdown on GitHub and GitLab, which makes it ideal for documentation that lives next to code. PlantUML has a far more complete UML feature set and finer control, but it renders through a Java server and is not drawn natively on GitHub. Pick Mermaid for quick docs-as-code, PlantUML for exhaustive UML.
Can Mermaid do everything PlantUML can?
No. PlantUML covers more UML diagram types and offers deeper styling and layout control. Mermaid covers the diagrams most teams need day to day — flowcharts, sequence, ER, class, state and Gantt — with much less syntax. If you need advanced UML such as detailed component or deployment diagrams, PlantUML goes further.
Is Graphviz the same as Mermaid?
No. Graphviz uses the DOT language and excels at automatically laying out large node-and-edge graphs — dependency trees, call graphs, state machines. Mermaid is higher-level and diagram-type aware (it knows what a sequence diagram is), and it renders in the browser and on GitHub. For a big generated graph, Graphviz’s layout engine is hard to beat; for readable docs diagrams, Mermaid is faster to write.
Does GitHub render PlantUML or Graphviz?
GitHub renders Mermaid natively in fenced ```mermaid blocks, but not PlantUML or Graphviz. For those, you generate an image (SVG or PNG) with their renderer and commit or link that image in your Markdown.
Can I convert PlantUML to Mermaid automatically?
There is no reliable one-click converter — the syntaxes and feature sets differ, so a clean conversion usually means rewriting the diagram by hand. The good news is that the common types (sequence, class, state) map closely, so a manual rewrite is quick for everyday diagrams.