# Module And Boundary Design

> Design module ownership and boundaries for one feature. Use when deciding where feature behavior, rules, data access, API handling, and UI responsibilities belong.

- Skill: `harsh817/module-and-boundary-design` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add harsh817/module-and-boundary-design`
- Raw SKILL.md: https://api.skillmd.com/api/skills/harsh817/module-and-boundary-design/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: harsh817 (https://skillmd.com/u/harsh817)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/harsh817/module-and-boundary-design

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# Module And Boundary Design

## Definition

Place feature knowledge in the modules best able to hide it. Boundaries should reduce cognitive load, avoid information leakage, and keep layers at distinct abstraction levels.

## Questions To Ask

- Which module owns this feature's domain rule?
- Which layer should know about UI state, API transport, persistence, and business policy?
- What must cross the boundary, and what must stay hidden?
- Are any new modules shallow wrappers?
- Does the feature require moving complexity downward?

## Existing Project Comparison

- Inspect existing modules, folders, imports, commands, services, and tests.
- Compare proposed boundaries with `AGENT_GUARDRAILS.md`.
- Identify duplicated rules, pass-through layers, and ownership conflicts.

## Suggestive Plan

1. Identify owner module.
2. List affected modules and responsibilities.
3. Define allowed dependency direction.
4. Mark hidden decisions per module.
5. Remove pass-through or shallow boundaries.

## Example

Scheduling owns appointment-window rules. API routes translate requests. UI manages form state. Data access persists scheduling state without owning scheduling policy.

## Vocabulary

- Boundary: line where modules or layers communicate.
- Owner module: module responsible for rules and decisions.
- Information hiding: keeping design knowledge inside the owner.
- Pass-through layer: layer that forwards without adding abstraction.

## Expected Outcome

Produce a boundary map with owner modules, responsibilities, hidden details, allowed dependencies, and boundary risks.