Night Market Skill — ported from claude-night-market/cartograph. For the full experience with agents, hooks, and commands, install the Claude Code plugin.

Data Flow Diagram

Generate a Mermaid sequence diagram showing how data moves between components in a codebase.

When To Use

• Tracing how a request flows through the system
• Understanding data transformation pipelines
• Documenting API call chains
• Answering "what happens when X is called?"

Workflow

Step 1: Explore the Codebase

Dispatch the codebase explorer agent:

Agent(cartograph:codebase-explorer)
Prompt: Explore [scope] and return a structural model.
Focus on function calls, data transformations, and
inter-module communication for a data flow diagram.

Step 2: Generate Mermaid Syntax

Transform the structural model into a Mermaid sequence diagram.

Rules for data flow diagrams:

• Use

  sequenceDiagram

  for request/response flows
• Participants are modules or components (not functions)
• Arrows show data direction:

  ->>

  for calls,

  -->>

  for returns
• Use

  activate

  /

  deactivate

  for long-running operations
• Add

  Note over

  for data transformations
• Limit to 8-10 participants maximum
• Use

  alt

  /

  else

  for conditional flows
• Handle circular calls by showing them once with a note

Example output:

sequenceDiagram
    participant User
    participant Command as /commit
    participant Sanctum as sanctum.commit
    participant Leyline as leyline.git_platform
    participant Git

    User->>Command: /commit
    Command->>Sanctum: generate_message()
    Sanctum->>Leyline: get_staged_changes()
    Leyline->>Git: git diff --cached
    Git-->>Leyline: diff output
    Leyline-->>Sanctum: structured changes
    Note over Sanctum: Classify change type
    Sanctum-->>Command: commit message
    Command->>Git: git commit -m "..."

Step 3: Render via MCP

Call the Mermaid Chart MCP to render:

mcp__claude_ai_Mermaid_Chart__validate_and_render_mermaid_diagram
  prompt: "Data flow diagram of [scope/feature]"
  mermaidCode: [generated syntax]
  diagramType: "sequenceDiagram"
  clientName: "claude-code"

If rendering fails, fix syntax and retry (max 2 retries).

Step 4: Present Results

Show the rendered diagram with a brief description of the flow depicted (2-3 sentences).