principle-model-the-domain

principle-model-the-domain is a skill for Claude Code from koolamusic/claudefiles. It costs 27 tokens per session (373 once invoked), scanned A, a copy of principle-model-the-domain, MIT.

A design guideline for representing real-world concepts with suitable data structures instead of spreading their rules across many conditions.

In plain words
What is it for?
Use it for stateful logic, lifecycle states, typed data, registries, queues, caches, and other code with repeated shape assumptions or many branches.
Why use it?
A clear model can prevent invalid states and reduce repeated branching. It also makes ownership and behaviour easier to understand as the code grows.

Skill for Claude Code

Written for Claude Code: disable-model-invocation in frontmatter.

Part of the pstack plugin — 50 skills, 2 agents shipped together

Good fit Use it for stateful logic, lifecycle states, typed data, registries, queues, caches, and other code with repeated shape assumptions or many branches.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/koolamusic/claudefiles/principle-model-the-domain
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add koolamusic/claudefiles --skill principle-model-the-domain
Clone the repo
git clone --depth 1 https://github.com/koolamusic/claudefiles

Made for: Claude Code.

Or install pstack, the plugin that ships this one along with the rest of its 50 skills, 2 agents.

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.

agentmods badge for principle-model-the-domain

README.md
[![agentmods](https://agentmods.dev/badge/skills/koolamusic/claudefiles/principle-model-the-domain/github.svg)](https://agentmods.dev/skills/koolamusic/claudefiles/principle-model-the-domain)
Your own site
<a href="https://agentmods.dev/skills/koolamusic/claudefiles/principle-model-the-domain"><img src="https://agentmods.dev/badge/skills/koolamusic/claudefiles/principle-model-the-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.

agentmods 80×15 button for principle-model-the-domain

Your own site · 80×15
<a href="https://agentmods.dev/skills/koolamusic/claudefiles/principle-model-the-domain"><img src="https://agentmods.dev/badge/skills/koolamusic/claudefiles/principle-model-the-domain.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 27 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 373 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.
Origin 94% copy Near-identical to another mod 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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00027 $0.00373
Opus 5.5 $0.00011 $0.00149
Sonnet 5.5 $0.00005 $0.00075
Haiku 4.5 $0.00003 $0.00037

Measured 2d ago against content hash 52c0d85e0c38, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

principle-model-the-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 2d 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.

Origin

This is a copy

94% identical to principle-model-the-domain — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

plugins/pstack/skills/principle-model-the-domain/SKILL.md · 25 lines

What it actually says

Model the Domain

Encode the real domain in a data structure instead of scattering it across conditionals. A structure that matches the domain makes invalid states unrepresentable and deletes branches. Choosing it at write time is cheap. Recovering it later reads as a refactor and gets deferred.

Reach for:

  • A state machine instead of scattered booleans, phases, or lifecycle checks.
  • A typed model instead of loose parameters or repeated shape assumptions.
  • A map, registry, lookup table, or discriminated union instead of branching spread across files.
  • A reducer or command/event model instead of ad hoc state mutations.
  • A module organized around one body of domain knowledge instead of a sequence such as load, validate, transform, and save. Execution order is not ownership.
  • A small module boundary that gathers repeated behavior, ownership, or invariants.
  • A queue, cache, index, graph, tree, or normalized collection where the access pattern calls for it.
  • Any other structure that fits. When none fits, work out what the code must never allow and how the data gets read, then find the structure that encodes exactly that.

Do not force an abstraction. Prefer boring code if the current shape is already clear, local, and unlikely to grow. Be skeptical of an abstraction that adds indirection without removing branches, duplicated rules, invalid states, or lifecycle risk.

The sign that you skipped this is a new feature that grows an existing if/else chain by one more branch, or a second boolean that must stay in sync with the first. Temporal decomposition is another sign. Phase-named modules repeat the same domain rules across steps.

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.

  1. 2d ago First seen · 25 lines · 27 tokens per session scan A 52c0d85e0c38

Subscribe to this mod's changes

principle-model-the-domain is a skill published in the GitHub repository koolamusic/claudefiles (130 stars, last pushed yesterday), licensed MIT. It adds 27 tokens to every session and 373 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 94% identical to principle-model-the-domain, differing in 0 lines, and is treated as a copy.

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