Mermaid Syntax Reference
Overview
Mermaid is a JavaScript-based diagramming tool that renders diagrams from Markdown-inspired text definitions. Diagrams render as SVG directly in browsers and are natively supported by GitHub, GitLab, Azure DevOps, Obsidian, and Notion.
Key advantages:
- Zero setup (browser-based rendering)
- Native Markdown integration (diagrams auto-sync with definitions)
- Simpler syntax than PlantUML
- No external dependencies
Limitations:
- Less customization than PlantUML
- C4 support is experimental
- No MindMap or JSON visualization
Diagram Types Quick Reference
| Type | Keyword | Best For |
|---|---|---|
| Flowchart | flowchart or graph | Process flows, decision trees, workflows |
| Sequence | sequenceDiagram | API calls, request/response flows |
| Class | classDiagram | OOP structures, inheritance, relationships |
| State | stateDiagram-v2 | State machines, lifecycle states |
| ER | erDiagram | Database schemas, entity relationships |
| Gantt | gantt | Project timelines, schedules |
| Pie | pie | Distribution, proportions |
| Git Graph | gitGraph | Branching strategies, commit history |
| C4 Context | C4Context | System architecture (experimental) |
| Timeline | timeline | Chronological events |
Markdown Integration
Mermaid diagrams are embedded in Markdown using fenced code blocks:
flowchart TD A[Start] --> B[End]
Platform support:
- GitHub: Native rendering in README, issues, PRs, wikis
- GitLab: Native rendering in Markdown files
- Azure DevOps: Native rendering in wikis and repos
- Obsidian: Native with core plugin
- VS Code: With Markdown Preview Mermaid Support extension
Quick Reference Card
Flowchart
flowchart TD
A[Box] --> B{Decision}
B -->|Yes| C[Action]
B -->|No| D[Other]Sequence
sequenceDiagram
A->>B: Request
B-->>A: ResponseClass
classDiagram
class Name {
+attribute type
+method() return
}
A <|-- B : inheritsState
stateDiagram-v2
[*] --> State1
State1 --> State2 : event
State2 --> [*]ER
erDiagram
ENTITY1 ||--o{ ENTITY2 : relationship
ENTITY1 {
type attribute PK
}References
For detailed syntax and complete examples, see:
| Reference | Content | When to Load |
|---|---|---|
| flowchart.md | Node shapes, edge types, subgraphs | Creating flowcharts |
| sequence.md | Participants, arrows, activation, alt/loop | Creating sequence diagrams |
| class.md | Classes, visibility, relationships, cardinality | Creating class diagrams |
| state-er.md | State machines, ER diagrams, relationships | Creating state/ER diagrams |
| special-diagrams.md | Gantt, Git Graph, C4, styling, gotchas | Creating special diagrams |
Test Scenarios
Scenario 1: Creating a flowchart
Query: "Create a Mermaid flowchart for user registration process"
Expected: Skill activates, provides flowchart syntax with decision nodes and subgraphs
Scenario 2: Creating a sequence diagram
Query: "Generate a Mermaid sequence diagram for API authentication"
Expected: Skill activates, provides sequence syntax with participants and alt/loop blocks
Scenario 3: Creating an ER diagram
Query: "Create a Mermaid ER diagram for a blog database"
Expected: Skill activates, directs to state-er.md reference for entity attributes and relationships
Last Updated: 2025-12-28 Mermaid Version: 10.x / 11.x
Version History
- v1.1.0 (2025-12-28): Refactored to progressive disclosure - extracted content to references/
- v1.0.0 (2025-12-26): Initial release