Mermaid Diagram

Mermaid.js is a JavaScript library for creating diagrams and flowcharts directly in the browser, using a concise, Markdown-inspired text syntax — a browser-native alternative to PlantUML Diagram's Java-based renderer, with especially strong support for embedding directly inside Markdown documents.

Diagram types

Flowcharts, sequence diagrams, Gantt charts, class diagrams, state diagrams, pie charts, and more — covering much of the same diagram-type territory as PlantUML Diagram (see Activity Diagram, Sequence Diagram, Class Diagram, State Diagram and this collection's other diagram-type skills for the underlying UML modeling concepts, independent of which text-based tool renders them).

Example syntax

flowchart TD
    A[Start] --> B{Decision}
    B -->|Yes| C[Do something]
    B -->|No| D[Do something else]
    C --> E[End]
    D --> E

sequenceDiagram
    Alice->>Bob: Hello Bob, how are you?
    Bob-->>Alice: I am good thanks!

The syntax reads close to plain English/Markdown — deliberately more approachable to non-technical readers than PlantUML's somewhat denser notation, which is part of why Mermaid has become the default choice for diagrams embedded directly in Markdown documentation.

Key characteristics

• Markdown-like syntax — concise and human-readable, approachable even for non-technical contributors editing documentation.
• Browser-based — runs entirely client-side with no server-side processing or external service dependency, making it easy to embed diagrams directly on a webpage.
• Live rendering — diagrams render in real time as the specification is written or edited, giving immediate visual feedback.
• Customization — colors, fonts, arrow styles, line thickness, and other visual attributes are all configurable.
• Broad integration — works in Markdown editors, CMSs, documentation tools, and general web applications; supports exporting to SVG or PNG.

Where Mermaid renders natively

Mermaid is supported directly (no extra library needed) in GitHub and GitLab Markdown (fenced `mermaid code blocks), and in this environment's own Artifacts (both Markdown `mermaid fences and inline <pre class="mermaid"> blocks in HTML) — making it the more convenient default choice specifically when a diagram needs to live inside a Markdown file or a web-rendered document, versus PlantUML Diagram, which more commonly needs a rendering step or plugin to produce an image.

Mermaid vs. PlantUML

Both are text-based diagram tools with overlapping diagram-type coverage. Mermaid favors approachability and native Markdown/web rendering; PlantUML (see PlantUML Diagram) offers a broader diagram-type catalog (C4 model, ArchiMate, WBS, mind maps, and more) and more fine-grained styling control at the cost of needing a Java-based renderer or plugin in most contexts. Choose based on where the diagram needs to live (embedded in Markdown/web → Mermaid; a broader modeling need, or an existing PlantUML-based toolchain → PlantUML) rather than assuming one is strictly better.

Common pitfalls

• Assuming full feature parity with PlantUML — Mermaid's diagram-type catalog, while substantial, is narrower than PlantUML's (no native ArchiMate or C4-model support, for instance); check current Mermaid documentation before assuming a specific PlantUML feature has a direct equivalent.
• Overly dense flowcharts — Mermaid's approachable syntax makes it easy to keep adding nodes; the same overcrowding warning Flowchart and Class Diagram give elsewhere applies here too.
• Forgetting the platform needs native Mermaid support — not every Markdown renderer supports Mermaid fences out of the box; verify the target platform (or add the JS library) before assuming a ​`mermaid block will render rather than show as a plain code block.

Learn more

• Mermaid.js documentation
• PlantUML Diagram for the alternative text-based diagramming tool with a broader diagram-type catalog.
• Flowchart, Sequence Diagram, Class Diagram, State Diagram for the underlying diagram-type modeling concepts, independent of rendering tool.