# Domain Modeling

> Build and sharpen a project's domain model. Use when discussing codebase terminology, writing, or editing a CONTEXT.md.

- Skill: `dmmulroy/domain-modeling` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add dmmulroy/domain-modeling`
- Raw SKILL.md: https://api.skillmd.com/api/skills/dmmulroy/domain-modeling/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: dmmulroy (https://skillmd.com/u/dmmulroy)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/dmmulroy/domain-modeling

---


# Domain Modeling

Actively build and sharpen the project's domain model as you design. This is the *active* discipline: challenging terms, inventing edge-case scenarios, and writing the glossary and decisions down the moment they crystallise. (Merely *reading* `CONTEXT.md` for vocabulary is not this skill: that's a one-line habit any skill can do. This skill is for when you're changing the model, not just consuming it.)

## File structure

Most repos have a single context:

```
/
├── CONTEXT.md
└── src/
```

Create files lazily: only when you have something to write. If no `CONTEXT.md` exists, create one when the first term is resolved.## During the session

### Challenge against the glossary

When the user uses a term that conflicts with the existing language in `CONTEXT.md`, call it out immediately. "Your glossary defines 'cancellation' as X, but you seem to mean Y. Which is it?"

### Sharpen fuzzy language

When the user uses vague or overloaded terms, propose a precise canonical term. "You're saying 'account': do you mean the Customer or the User? Those are different things."

### Discuss concrete scenarios

When domain relationships are being discussed, stress-test them with specific scenarios. Invent scenarios that probe edge cases and force the user to be precise about the boundaries between concepts.

### Cross-reference with code

When the user states how something works, check whether the code agrees. If you find a contradiction, surface it: "Your code cancels entire Orders, but you just said partial cancellation is possible. Which is right?"

### Update CONTEXT.md inline

When a term is resolved, update `CONTEXT.md` right there. Don't batch these up: capture them as they happen. Use the format in [CONTEXT-FORMAT.md](./CONTEXT-FORMAT.md).

`CONTEXT.md` should be totally devoid of implementation details. Do not treat `CONTEXT.md` as a spec, a scratch pad, or a repository for implementation decisions. It is a glossary and nothing else.