Ready to supercharge your AI agents?

Install any skill in seconds. Free to start, no credit card required.

Model the Domain · michael-denyer | DecimalAI

codingby michael-denyer

Model the Domain

michael-denyer/principle-model-the-domain

Source michael-denyer/pstack-claude ↗License MIT

Apply when writing stateful logic, or when code branches a lot or repeats a shape assumption across files. Encode the domain in a structure instead of scattered conditionals.

NewMaintained

Automatic

Coding pack

Last verified 10/10/2026

What it changes

Passed 21 of 23 test cases with the skill, and 21 of 23 without it.

Without skill91%

With skill91%

Checks it passed that the model alone missed

Eliminates phase-named files organized by execution sequence.
Consolidates temporal phase modules into a domain boundary organized around the order entity.

1 fixed20 passed either way1 still failing1 broke

Pass-rate lift: 0 pp
Tokens: +6%
Agent turns: 0%
Response time: -5%

Model gemini-3.6-flashMeasured 10/10/2026v121 of 23 cases passed with skill

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/michael-denyer-principle-model-the-domain/SKILL.md https://app.decimal.ai/s/michael-denyer-principle-model-the-domain/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add michael-denyer-principle-model-the-domain, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/michael-denyer-principle-model-the-domain/ and pins it in .decimal/skills.lock

decimalai skills add michael-denyer-principle-model-the-domain

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/michael-denyer-principle-model-the-domain/SKILL.md https://app.decimal.ai/s/michael-denyer-principle-model-the-domain/SKILL.md

Raw file: /s/michael-denyer-principle-model-the-domain/SKILL.md ↗ · machine-readable summary at /s/michael-denyer-principle-model-the-domain.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

A test case the skill fixed. Same model, same prompt, with and without the skill.

Prompt

We have an order processing backend in Python split into `order_loader.py`, `order_validator.py`, `order_transformer.py`, and `order_saver.py`. We need to add a fraud check step. Redesign the file and module organization for this order processing system.

What was checked, without and with the skill
Checked	Without skill	With skill
Consolidates temporal phase modules into a domain boundary organized around the order entity.	Missed	Passed
Eliminates phase-named files organized by execution sequence.	Missed	Passed

case-02 · gemini-3.6-flash · 10/10/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md20 linessingle file

Model the Domain

Encode the real domain in a data structure instead of scattering it across conditionals.

Why: Scattered booleans, repeated shape assumptions, and branching spread across files are accidental complexity. 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 structures like these:

A state machine instead of scattered booleans, phases, or lifecycle checks.
A typed object/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 data 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.

Track record

Benchmark

21 / 23

test cases passed, vs 21 / 23 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v5 — 9/15/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

michael-denyer / pstack-claude

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

View on GitHub ↗

License MITImported 9/15/2026Version v1

Other skills for the same job

Published skills whose descriptions closely match this one, with their headline benchmark lift.

cursor/principle-model-the-domainApply when writing stateful logic, or when code branches a lot or repeats a shape assumption across files. Encode the domain in a structure instead of scattered conditionals.Near-identical description+13 pp pass-rate lift

More skills from the same source and nearby in the registry, with their headline benchmark lift.

Ready to supercharge your AI agents?

See it in action

What's inside

Model the Domain

Track record

Benchmark

Adoption

SkillSafety

Source

Other skills for the same job

Related skills