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:

/
├── 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:

/
├── 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.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.

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.