---
name: domain-modeling
description: >
  Build and sharpen a project's domain model. Use when pinning down domain
  terminology or ubiquitous language, recording an architectural decision, or
  when another skill (for example grill-with-docs) needs to maintain the domain
  model. Also use when the repo declares short living alignment docs under
  docs/agents/ that should stay current as terms and constraints crystallise.
---

# 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* `GLOSSARY.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:

```text
/
├── GLOSSARY.md
├── docs/
│   └── adr/
│       ├── 0001-event-sourced-orders.md
│       └── 0002-postgres-for-write-model.md
└── src/
```

If a `GLOSSARY-MAP.md` exists at the root, the repo has multiple contexts. The map
points to where each one lives:

```text
/
├── GLOSSARY-MAP.md
├── docs/
│   └── adr/                          ← system-wide decisions
├── src/
│   ├── ordering/
│   │   ├── GLOSSARY.md
│   │   └── docs/adr/
│   └── billing/
│       ├── GLOSSARY.md
│       └── docs/adr/
```

Create files lazily — only when you have something to write. If no `GLOSSARY.md`
exists, create one when the first term is resolved. If no `docs/adr/` exists,
create it when the first ADR is needed.

## During the session

### Challenge against the glossary

When the user uses a term that conflicts with the existing language in
`GLOSSARY.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 precision about
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.

### Update GLOSSARY.md inline

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

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

### Offer ADRs sparingly

Only offer to create an ADR when all three are true:

1. **Hard to reverse** — the cost of changing your mind later is meaningful
2. **Surprising without context** — a future reader will wonder why it was done
   this way
3. **The result of a real trade-off** — there were genuine alternatives and you
   picked one for specific reasons

If any of the three is missing, skip the ADR. Use the format in
[ADR-FORMAT.md](./ADR-FORMAT.md).

## Living short alignment docs (optional)

Some repos declare short living alignment files (environment map, landmines,
definition of done / evidence, golden-path smoke, pins, owns/asks) so agents do
not rediscover the same facts every session.

1. Read `docs/agents/domain.md` if it exists (or another repo-local domain index).
2. If that file names paths for short living docs, create or update those files
   when the relevant fact crystallises — same discipline as GLOSSARY/ADR: short
   bullets, one screen when possible, no essay piles.
3. If the repo does not declare those paths, do **not** invent a new docs tree.
   Stick to `GLOSSARY.md` and `docs/adr/`.

Examples of living-short content (only when the repo asks for them):

environment map, never-do landmines, work-type evidence / DoD, golden-path smoke
checklists, current pins, owns/asks.

## Source

First-party adaptation of the domain-modeling skill previously used via
mattpocock/skills, owned here so it can evolve with AnthonyPoschen/agent-skills.