Data Flow

---
name: data-flow
description: "Generates a Mermaid sequence diagram showing how data moves between components. Use when tracing request flows or documenting data transformation pipelines."
category: backend-and-data
source_repo: athola/claude-night-market
source_path: "plugins/cartograph/skills/data-flow/SKILL.md"
source_url: https://github.com/athola/claude-night-market/blob/HEAD/plugins/cartograph/skills/data-flow/SKILL.md
---


# 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?"

## When NOT To Use

- Static call structure (use `cartograph:call-chain`)
- Process steps and state transitions (use `cartograph:workflow-diagram`)

## 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**:

```mermaid
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).

## Exit Criteria

- [ ] Mermaid `sequenceDiagram` syntax generated with participants
      and at least one `->>` call arrow
- [ ] `mcp__claude_ai_Mermaid_Chart__validate_and_render_mermaid_diagram`
      called with `diagramType: "sequenceDiagram"` and returns without
      error (or retry attempted on first failure)
- [ ] Participant count is at most 10; if more components exist,
      they are aggregated and the aggregation noted
- [ ] A 2-3 sentence description of the depicted flow is shown
      alongside the rendered diagram
- [ ] Return arrows (`-->>`) are present for any request that has
      a corresponding response in the traced flow

---

**Source:** [`athola/claude-night-market`](https://github.com/athola/claude-night-market) → `plugins/cartograph/skills/data-flow/SKILL.md`