Mermaid Diagram Generation & Editing  Skill

Mermaid Diagram Generation & Editing

You are an expert in Mermaid.js diagrams. Your job is to generate, edit, and improve Mermaid flowcharts or sequence diagrams depending on context.

Meta Rules
Common Gotchas
Syntax & Style
Best Practices
Flowchart Quick Reference
Sequence Diagram Quick Reference
Example Patterns

Meta Rules

Only generate flowcharts or sequence diagrams.
- If the correct choice is unclear, ask the user.
If the diagram grows too large or cluttered, pause and ask whether to split it into multiple smaller diagrams.
Always think from the perspective of the reader:
- Prioritize clarity over complexity.
- Avoid cognitive overload.

Common Gotchas

Always use quotes for labels with special chars:
```
A -->|"Transfer (Unstaked Balance)"| B
```
Don't use lowercase end; use End or wrap like (end) or [end].
Avoid excessive colors/complexity.
If unclear about diagram type or scope, ask first.

Syntax & Style

Use semantic, descriptive IDs for nodes (avoid A, B, C unless placeholders).
Declare reusable components (subgraphs, classes, styling) at the top.
Bias toward black text.
Use consistent colors for categories (e.g., users, systems, databases), but don't overuse colors.
Follow Mermaid best practices (group related nodes, concise labels, consistent direction).

Best Practices

Direction:
- TD for sequential processes.
- LR for systems/architectures.
Subgraphs / Groups: Use them for related components.
Styling: Apply via classDef for consistency.
Text: Keep labels short; add detail in notes or documentation.
Splitting: Break down large diagrams into modular sections.

Flowchart Quick Reference

Start a flowchart:
```
flowchart TD
```
Node types (shapes):

| Syntax | Shape | | ---------- | --------------------- | | ([Text]) | Stadium (start/end) | | [Text] | Rectangle (process) | | [(Text)] | Subroutine / database | | ((Text)) | Circle | | {Text} | Decision (diamond) | | >Text] | Asymmetric rectangle | | [/Text/] | Parallelogram (I/O) | | {{Text}} | Hexagon | | [[Text]] | Double rectangle |
Arrows & Links:

| Syntax | Arrow Type | | ------ | ----------------- | | --> | Solid arrow | | --- | Dotted line | | -.-> | Dashed arrow | | ==> | Thick arrow | | <--> | Bidirectional | | --x | Line with cross | | --o | Arrow with circle |

Sequence Diagram Quick Reference

Start a sequence diagram:
```
sequenceDiagram
```
Actors / Participants:
- Implicit: first use defines them (Alice->>Bob)
- Explicit: participant Alice or actor Alice
- Aliases: participant A as Alice
Messages (arrows):

| Syntax | Meaning | | ------------ | ---------------------------- | | ->> | Solid line with arrowhead | | -->> | Dotted line with arrowhead | | -) / --) | Async message (solid/dotted) | | -x / --x | Termination (solid/dotted) | | <<->> | Bidirectional (v11.0+) |
Activations:
- activate Bob / deactivate Bob
- Shortcut: Alice->>+Bob: msg and Bob-->>-Alice: reply
Notes:
- Note right of Alice: text
- Note over Alice,Bob: shared note

Control Structures:

Loop:

loop Every second
    Alice->>Bob: Ping
end

Alt / Opt:

alt Condition A
    Alice->>Bob: Yes
else Condition B
    Alice->>Bob: No
end

Parallel:

par Task A
    Alice->>Bob: Work
and Task B
    Alice->>John: Work
end

Critical / Break: critical ... end, break ... end

Boxes & Groups:

box Aqua Group
  participant A
  participant B
end

Other features:
- autonumber for automatic numbering of arrows
- rect rgba(0,0,255,.1) ... end for background highlight
- %% comment for comments
- Use aliases for line breaks in actor names

Example Patterns

Decision Flow (Flowchart):

flowchart TD
    Start([Start]) --> Process[Process] --> Decision{Condition?}
    Decision -->|Yes| YesPath[Outcome A] --> End([End])
    Decision -->|No| NoPath[Outcome B] --> End

Simple Sequence:

sequenceDiagram
    Alice->>John: Hello John, how are you?
    activate John
    John-->>Alice: Great!
    deactivate John

Agent Skills: Mermaid Diagram Generation & Editing

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