flow-diagram

Flow Diagram Skill

Create flow diagrams as Mermaid — text-based with automatic layout. Mermaid is diffable, cheap to generate, and renders natively in GitHub markdown (READMEs, PR and issue descriptions), Claude artifacts, and most docs tooling.

For graphs with fewer than 3 nodes or no edges, prefer plain text (ASCII or a markdown table) — not worth a diagram.

Workflow

1. Pick the diagram type

Data	Mermaid type
Flows, pipelines, decision branches	flowchart TD (or LR for wide/shallow graphs)
State machines	stateDiagram-v2
Dependencies, architecture maps	flowchart LR with subgraph groupings
Sequences of calls between systems	sequenceDiagram

2. Write the diagram

flowchart TD
    Welcome["Welcome message"] --> Hours{"Business hours?"}
    Hours -->|open| Queue["Route to Sales queue"]
    Hours -->|closed| AfterHours["After-hours message"]
    AfterHours --> Offer{"Leave a voicemail?"}
    Offer -->|yes| Record["Record voicemail"]
    Offer -->|no| Finish["End call"]
    Queue --> Finish
    Record --> Finish

Syntax gotchas:

• Quote any label containing parentheses, colons, or other punctuation: A["Play message (after hours)"]
• end (lowercase) is a reserved word in flowcharts — use a different node id like Finish
• Edge labels use pipes: A -->|open| B
• Colour node categories with classDef + class, e.g. classDef queue fill:#1d4ed8,color:#fff then class Queue queue

3. Deliver it where it will actually render

Mermaid source is only a picture where something renders it. A fenced block printed into a Claude Code terminal shows as raw source text, not a diagram — so pick the delivery form from the destination:

Destination	Deliver as
GitHub PR or issue description, README, a committed .md file	Fenced ```mermaid block — inline in the response for the user to paste, or written to the file
The user wants to look at the diagram now, in a Claude Code session ("show me", "let me see it")	A standalone HTML file they can open (section 5), or a published Artifact — never bare source in the terminal
Web or desktop chat, or docs tooling that renders Mermaid	Fenced ```mermaid block