A guide to domain modeling, the practice of representing a business problem in code. It explains concepts such as entities, value objects, aggregates, repositories, domain events, services, and business rules in Rust.

Use it when designing business models, deciding whether data needs identity, defining validation rules, setting ownership boundaries, or choosing repository and event patterns.

It helps choose suitable Rust types and ownership patterns so that business rules and valid states are enforced in the code.

How moeru-ai/auv configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to moeru-ai/auv. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/moeru-ai/auv/main/.agents/skills/m09-domain/SKILL.md

Clone the repo

git clone --depth 1 https://github.com/moeru-ai/auv

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/moeru-ai/auv/m09-domain/github.svg)](https://agentmods.dev/skills/moeru-ai/auv/m09-domain)

Your own site

<a href="https://agentmods.dev/skills/moeru-ai/auv/m09-domain"><img src="https://agentmods.dev/badge/skills/moeru-ai/auv/m09-domain/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/moeru-ai/auv/m09-domain"><img src="https://agentmods.dev/badge/skills/moeru-ai/auv/m09-domain.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 55 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 999 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00055	$0.00999
Opus 5.5	$0.00022	$0.00400
Sonnet 5.5	$0.00011	$0.00200
Haiku 4.5	$0.00006	$0.00100

Measured 2mo ago against content hash a05f32b475b0, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

m09-domain scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.agents/skills/m09-domain/SKILL.md · 175 lines

How it starts

The opening of the file, as written. The whole thing — 175 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Domain Modeling

Layer 2: Design Choices

Core Question

What is this concept's role in the domain?

Before modeling in code, understand:

Is it an Entity (identity matters) or Value Object (interchangeable)?
What invariants must be maintained?
Where are the aggregate boundaries?

Domain Concept → Rust Pattern

Domain Concept	Rust Pattern	Ownership Implication
Entity	struct + Id	Owned, unique identity
Value Object	struct + Clone/Copy	Shareable, immutable
Aggregate Root	struct owns children	Clear ownership tree
Repository	trait	Abstracts persistence
Domain Event	enum	Captures state changes
Service	impl block / free fn	Stateless operations

Thinking Prompt

Before creating a domain type:

What's the concept's identity?
- Needs unique identity → Entity (Id field)
- Interchangeable by value → Value Object (Clone/Copy)
What invariants must hold?
- Always valid → private fields + validated constructor
- Transition rules → type state pattern
Who owns this data?
- Single owner (parent) → owned field
- Shared reference → Arc/Rc
- Weak reference → Weak

Trace Up ↑

To domain constraints (Layer 3):

"How should I model a Transaction?"
    ↑ Ask: What domain rules govern transactions?
    ↑ Check: domain-fintech (audit, precision requirements)
    ↑ Check: Business stakeholders (what invariants?)

Design Question	Trace To	Ask
Entity vs Value Object	domain-*	What makes two instances "the same"?
Aggregate boundaries	domain-*	What must be consistent together?
Validation rules	domain-*	What business rules apply?

Trace Down ↓

To implementation (Layer 1):

"Model as Entity"
    ↓ m01-ownership: Owned, unique
    ↓ m05-type-driven: Newtype for Id

"Model as Value Object"
    ↓ m01-ownership: Clone/Copy OK
    ↓ m05-type-driven: Validate at construction

"Model as Aggregate"
    ↓ m01-ownership: Parent owns children
    ↓ m02-resource: Consider Rc for shared within aggregate

Read the full file on GitHub · 175 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2mo ago First seen · 175 lines · 55 tokens per session scan A a05f32b475b0

Subscribe to this mod's changes

m09-domain is a skill published in the GitHub repository moeru-ai/auv (203 stars, last pushed 2d ago), licensed Apache-2.0. It adds 55 tokens to every session and 999 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Backend and APIs Planning agent-desktop computer-use cua gui-automation os-automation phone-use

m09-domain next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
m09-domainmoeru-ai/auv	Skill	203	2d ago	Apache-2.0	A	55	Claude Code
telegramrazzant/ouroboros	Skill	1.6k	today	MIT	A	19	Claude Code
computer-use-safetyellmos-ai/skills	Skill	9	3d ago	MIT	A	186	Claude Code, Codex
open-compute-bridgeellmos-ai/skills	Skill	9	3d ago	MIT	B	149	Claude Code, Codex
oswrightAsk-812/oswright	Skill	4	21d ago	MIT	A	97	Claude Code, Codex
axstreammilind-soni/axstream	Skill	20	2mo ago	MIT	A	96	Claude Code
computer-useedosulai/silenthand-cua	Skill	0	2mo ago	MIT	A	37	Claude Code, Codex

auv: Skill for Claude Code