Mermaid vs PlantUML guide（繁體）
本指南說明 Mermaid vs PlantUML guide 的核心做法，幫助你更快從需求到可編輯圖表。
What is diagram-as-code?
Diagram-as-code means defining a diagram using a textual DSL (domain-specific language) rather than a GUI. The text is checked into version control alongside your code, which means diagrams can be reviewed in pull requests, diffed between versions, and kept in sync with the systems they describe.
The main tradeoff is that you lose WYSIWYG editing — you can't drag a box to reposition it. But for technical diagrams that change frequently, diagram-as-code wins because it removes the manual effort of maintaining a GUI diagram file.
Mermaid: strengths and syntax
Mermaid's biggest advantage is native GitHub rendering. Paste a Mermaid code block into any GitHub README, issue, or PR description and GitHub renders it as an interactive diagram — no external tool required. GitLab, Notion, Obsidian, and many other tools also support Mermaid natively.
Mermaid's syntax is minimal and readable. A flowchart with three nodes is three lines: `flowchart LR\nA[Start] --> B[Process] --> C[End]`. The supported diagram types include flowcharts, sequence diagrams, class diagrams, state diagrams, ERDs, Gantt charts, and git graphs.
Mermaid's weaknesses: layout control is limited (you can specify direction but not exact positions), complex diagrams can produce cluttered auto-layouts, and some advanced UML features (like interaction fragments in sequence diagrams) are not supported.
PlantUML: strengths and syntax
PlantUML supports a broader set of diagram types than Mermaid — including deployment diagrams, component diagrams, timing diagrams, and Archimate. For teams using the full UML spectrum or C4 architecture notation, PlantUML is more capable.
PlantUML's syntax is more verbose but also more expressive. You can control layout with `together` blocks, specify skin parameters to customize styling, and use `!include` for modular diagram composition — useful for large-scale architecture documentation.
PlantUML requires a Java runtime or a remote rendering server, which adds friction compared to Mermaid's pure-JavaScript rendering. Most CI/CD pipelines support PlantUML via a Docker image or the PlantUML JAR, but it's an extra dependency to manage.
Which should you choose?
Choose Mermaid if your diagrams live in GitHub/GitLab READMEs, Notion docs, or Obsidian notes, and you primarily need flowcharts and sequence diagrams. The zero-setup rendering and native integrations make it the lowest-friction option for most teams.
Choose PlantUML if you need C4 architecture diagrams, full UML compliance, or highly customized styling. PlantUML's expressiveness is worth the extra setup for organizations that treat architecture documentation as a first-class artifact.
Use AIDrawIO when you want to skip writing diagram-as-code entirely: describe the diagram in plain English, get Mermaid or PlantUML back as output, or export directly to draw.io XML. You can use the generated code as a starting point and edit from there.
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常見問題
Does GitHub support Mermaid diagrams natively?
Yes. GitHub renders Mermaid diagrams in Markdown files, issues, and pull request descriptions. Wrap your Mermaid code in a fenced code block with the language set to 'mermaid' (```mermaid) and GitHub renders it automatically.
Can PlantUML run without a server?
Yes. You can run PlantUML locally using the JAR file (requires Java). Many editors have PlantUML plugins (VS Code, IntelliJ) that render locally. There's also a public rendering server at plantuml.com, but it's rate-limited for large diagrams.
Is there an AI tool that writes Mermaid or PlantUML for me?
Yes. AIDrawIO's Mermaid editor and PlantUML editor accept a plain-English description and generate the corresponding diagram code. You can copy the generated code into your documentation or edit it as a starting point.
Which tool has better support for C4 architecture diagrams?
PlantUML has the C4-PlantUML library, which is widely used for C4 model documentation. Mermaid has basic C4 support but it's less mature. For C4 diagrams specifically, PlantUML is the better choice.