Mermaid vs PlantUML
Mermaid and PlantUML are the two leading diagram-as-code tools. Mermaid renders natively in GitHub, Notion, and Obsidian with a JavaScript-based renderer. PlantUML uses a Java server and its own syntax. Here's how they compare for real-world use.
Mermaid wins: 7
PlantUML wins: 1
Tie: 2
Feature Comparison
| Feature | Mermaid Editor | PlantUML | |
|---|---|---|---|
| GitHub Markdown rendering | Native — diagrams render in READMEs, issues, PRs | Not supported — requires image generation | |
| Setup required | None — runs in the browser via JS | Requires Java runtime or a server | |
| Diagram types | 20+ types including flowchart, sequence, ER, Gantt, mindmap, sankey | 15+ types including activity, component, deployment, timing | |
| Syntax style | Markdown-like, concise | Verbose, keyword-heavy | |
| UML compliance | Partial — class, sequence, state diagrams | Full UML 2.x compliance | |
| Rendering speed | Fast — client-side JavaScript | Slower — requires server round-trip | |
| Theming | CSS-based theme variables, custom color palettes | Skinparam system, extensive but complex | |
| Platform support | GitHub, GitLab, Notion, Obsidian, VS Code, Docusaurus | Confluence (plugin), VS Code (plugin), limited native support | |
| npm weekly downloads | 3M+ weekly downloads | ~50K weekly downloads | |
| Community size | 86K+ GitHub stars | 10K+ GitHub stars |
Our Verdict
Mermaid wins for most developers. It renders natively where you work (GitHub, Notion, Obsidian), requires zero setup, and has a simpler syntax. PlantUML is the better choice if you need strict UML compliance or specific diagram types like deployment or component diagrams. For database schemas, flowcharts, and documentation diagrams, Mermaid is the modern default.
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