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name: mermaid-builder description: Expert guidance for creating syntactically correct Mermaid diagrams. Use when creating flowcharts, sequence diagrams, class diagrams, state diagrams, Gantt charts, ER diagrams, or data lineage visualizations. allowed-tools: Read, Write, Edit, MultiEdit, Grep, Glob, Bash, WebSearch, WebFetch

Mermaid Builder

Core Philosophy

• Correctness: Follow Mermaid syntax rules strictly
• Clarity: Diagrams communicate complex ideas simply
• Simplicity: Avoid overloading with unnecessary detail
• Modularity: Break complex diagrams into subgraphs

Critical: Label Quoting Rule

RULE: Wrap labels in double quotes if they contain spaces, special characters, or punctuation.

%% CORRECT - labels with spaces quoted
flowchart LR
    A["User Login"] --> B["Process Request"]
    C["Pay $100?"] --> D["Confirm (Yes/No)"]

%% WRONG - will fail to render
flowchart LR
    A[User Login] --> B[Process Request]

Must quote: Spaces, special chars ($%&), punctuation (:,;), operators (()[]) Optional: Simple alphanumeric (Login, Process, Node1)

When in doubt, use quotes. It never hurts.

Quick Reference

Flowchart Shapes

Syntax	Shape
["Text"]	Rectangle
("Text")	Rounded
{"Text"}	Diamond (decision)
[("Text")]	Cylinder (database)
(("Text"))	Circle

Arrow Types

Syntax	Type
-->	Solid arrow
---	Solid line
-.->	Dotted arrow
==>	Thick arrow
`-->	Label

Diagram Types

Type	Declaration	Use Case
Flowchart	flowchart TD	Processes, workflows, decisions
Sequence	sequenceDiagram	Component interactions, API flows
Class	classDiagram	OOP structure, models
State	stateDiagram-v2	State transitions
Gantt	gantt	Timelines, scheduling
ER	erDiagram	Database schema
Pie	pie	Proportional data

Directions: TB/TD (top-down), BT (bottom-up), LR (left-right), RL (right-left)

See resources/diagram-examples.md for complete examples of each diagram type.

Minimal Examples

Flowchart

flowchart TD
    Start["Start"] --> Check{Valid?}
    Check -->|Yes| Process["Process"]
    Check -->|No| Error["Error"]
    Process --> End["End"]

Sequence

sequenceDiagram
    Client->>Server: Request
    Server-->>Client: Response

ER Diagram

erDiagram
    USER ||--o{ ORDER : "places"
    USER { int id PK string email }
    ORDER { int id PK int user_id FK }

Subgraphs for Organization

flowchart TD
    subgraph "Frontend"
        A["UI"]
    end
    subgraph "Backend"
        B["API"]
        C[("DB")]
    end
    A --> B --> C

Styling

flowchart TD
    A["Success"] --> B["Error"]

    classDef successStyle fill:#C8E6C9,stroke:#388E3C
    classDef errorStyle fill:#FFCDD2,stroke:#D32F2F

    class A successStyle
    class B errorStyle

Common Errors to Avoid

Error	Wrong	Correct
Unquoted spaces	A[User Login]	A["User Login"]
Invalid arrow	A -> B	A --> B
Unquoted special	A[Cost: $100]	A["Cost: $100"]
Missing bracket	A["Node --> B	A["Node"] --> B

Validation Checklist

• Labels with spaces are quoted
• Labels with special characters quoted
• Brackets properly matched
• Arrow syntax correct (--> not ->)
• Node IDs unique and meaningful
• Comments explain complex sections
• Previewed without errors

Data Lineage Patterns

See resources/data-lineage.md for:

• ETL pipeline patterns
• Multi-layer data architecture
• Cross-system data flows
• Database schema lineage
• Streaming data lineage
• Column-level lineage

Resources

• Mermaid Docs
• Live Editor
• Syntax Reference

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Remember: The quoting rule is the #1 cause of Mermaid rendering failures. When in doubt, quote it.