Data Modeling Agent Skill

Make the arbitrary decisions in a schema explicit — what makes two records the same thing, whether a row is one thing or several, when a…

Context cost
6.1k tokensestimated from the bundle, loaded when it triggers
Bundle
4 files · 24.3 kBtext throughout, nothing executable
Licence
MITthe author’s own terms
Last change
—no release on file
Servers it uses
Noneruns standalone

What it does

Make the arbitrary decisions in a schema explicit — what makes two records the same thing, whether a row is one thing or several, when a value should be a column versus its own table, what a category means at its edges, and what identity survives change. Use when designing or reviewing a schema, choosing a primary key, adding a status enum, modelling history or versioning, or integrating data from two systems that name things differently.

What this skill changes about the agent has not been set out here as a list. Its SKILL.md, shown below, says it in the author’s own words.

database
Filed under

Databases

The skill itself

A skill is instructions the model reads, so you can see what you are getting: below is the start of its SKILL.md. The front matter loads with every session, the body loads when the skill triggers, and the whole file comes with the install.

SKILL.md6.5 kB · preview
--- name: data-modeling ---
6# Data Modeling
7
8## Purpose
9
10A schema is not a discovery of structure that was already there. It is a series of arbitrary, purpose-driven decisions about how to represent a domain — and almost all of them get made implicitly, by whoever happened to write the migration.
11
12The failures that follow are recognisable: two teams reading the same column differently, a count that disagrees with reality, a rename that looks like a delete-and-recreate, a category with no slot for the record that just arrived. In each case the decision was never wrong exactly — it was never *made*.
13
14This skill is about surfacing those decisions while they're still cheap.
15
16## An awkward shape is a missing concept
17
18The same surfacing habit applies one layer up, in code. When a type grows its Nth optional field or its Nth variant and each one "shouldn't be necessary," that is a signal a concept is missing from the domain vocabulary — not a modelling problem to push through by adding another field.
19
20Stop and ask what single entity would make the awkwardness disappear, and take the resulting question back to whoever owns the business rule. *Does "primary contact method" mean anything, and can two be equally primary?* is a requirements question the type shape surfaced, not an implementation detail to settle alone.
21
22## Rules that apply without loading anything
23
24**1. Separate identity from name.** A primary key must not be something that can legitimately change while the thing stays the same thing. Use an opaque surrogate; treat codes, emails, and names as ordinary mutable attributes. Otherwise a rename cascades through every referencing table — or gets faked as a delete-and-reinsert, which silently severs history.
This is a preview of SKILL.md. Download or install the skill to get the whole thing.
In the file
SKILL.md1,057 words
Files4
LicenceMIT
Why you can read it

Nothing in a skill executes. The client loads the text and the model follows it, so a skill can be audited the way a runbook is — by reading it.

What it costs in context

Skills are not billed by the call. They are paid for in context: every token the instructions occupy is a token your code, your diff and your conversation cannot use. Here is what this one takes and when it takes it.

≈120
always loaded
The name and description, so the model knows the skill exists and when to reach for it.
5,955
on trigger
The instruction body and 3 supporting files, read only when the skill fires.
3.0%
of a 200k window
Ten skills this size would take about 30% of the window before you open a file.
050k100k150k200k context window

6.1k tokens, estimated from the bundle at four bytes to the token, held for the rest of the session once it triggers. Heavy. Teams tend to install this one per project rather than globally, and load it only when the job comes up.

Servers bill, skills cost

A server charges by the month. A skill charges once per session, in context, and then keeps charging it for as long as the session lives.

Before and after

The same question, put to the same model twice: once as it comes, and once with these instructions loaded.

No worked example has been published for this skill yet.

The procedure it runs

The procedure has not been set out here step by step. It is in the body of its SKILL.md: the start of it is shown above, and the whole file comes with the install.

Prose, not code

These steps are written for a model to follow, not executed by a runtime. It can still be told to skip one, and it will say so when it does.

Servers it uses

None. This skill calls no MCP servers at all.

Everything it needs is in the instructions, so it works in a project with nothing connected — the model reads the file and changes how it works with what it can already reach.

Its SKILL.md does not declare which tools it asks the agent for, so what it touches is whatever the instructions themselves ask for — read them before you install it.

What it asks for
Writes filesnot declared
Network accessnot declared

This SKILL.md carries no allowed-tools line, so neither is declared. A skill grants no permissions of its own — it can only ask for tools your client already has.

What it will not do

Every skill is narrow, and the useful ones say where they stop. These are the jobs this one is the wrong tool for.

What this skill is not for has not been published here. Nothing is implied by that: it is a section the author has not filled in.

What is in the bundle

4 files, 24.3 kB on disk. A bundle is text throughout: the instructions the model reads, plus the templates it fills in.

  • SKILL.md6.5 kB
  • references/categories-and-change.md7.3 kB
  • references/identity.md5.7 kB
  • references/structure.md4.8 kB
What is not in it

No dependencies and nothing executable: a skill is text the agent reads, so the bundle is 4 files you can review in full before installing. The MIT licence covers the templates and examples as well as the instructions.

Install

Installing copies the bundle into your project. Nothing runs at install time — the files sit on disk until the model reads them.

# Data Modeling · 6.1k tokens when loaded · macOS, Linux mkdir -p .claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/plunderstruck-data-modeling/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/data-modeling" ] && { [ ! -e .claude/skills/data-modeling ] || { mv .claude/skills/data-modeling "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/data-modeling" .claude/skills/ && echo "Installed .claude/skills/data-modeling"
On Windows, or any OS with Node 20+
npx mcprush@latest skill add plunderstruck/data-modeling

Windows PowerShell says 'running scripts is disabled on this system'? Run Set-ExecutionPolicy -Scope CurrentUser RemoteSigned once, or type npx.cmd instead of npx (codex.cmd, gemini.cmd, grok.cmd likewise). PowerShell 7 needs neither. Writes to .claude/skills/data-modeling/ in the current project. For every project instead, run mkdir -p ~/.claude/skills && t=$(mktemp -d) && curl -fsSL -o "$t/bundle.tar.gz" https://mcprush.com/api/skills/plunderstruck-data-modeling/bundle.tar.gz && tar -xzf "$t/bundle.tar.gz" -C "$t" && [ -d "$t/data-modeling" ] && { [ ! -e ~/.claude/skills/data-modeling ] || { mv ~/.claude/skills/data-modeling "$t/.previous" && echo "Previous copy moved to $t/.previous"; }; } && mv "$t/data-modeling" ~/.claude/skills/ && echo "Installed ~/.claude/skills/data-modeling" (macOS, Linux) — or add --global to the npx line. The curl line replaces .claude/skills/data-modeling/ only after the download succeeds, so files left there by another skill of the same name, or by an older release, do not mix in. A copy already there is moved aside, not deleted, and the line prints where.

Which clients pick it up on their own

A skill is a folder of text. Most of these read a skills folder and pick it up without being told; the rest take the same folder another way — an upload in the app, a parameter on an API call — and then choose it by its description just the same.

Claude Code.claude/skills/
Claude DesktopCustomize › Skills
ChatGPTSkills › Create › Upload
Cursor.cursor/skills/
VS Code.github/skills/
Codex CLI.agents/skills/
Gemini CLI.gemini/skills/
Grok Build.grok/skills/
Microsoft CopilotSkills › Upload a skill
PerplexityComputer › Skills › Upload a skill
DeepSeek Harness.dsh/skills/
Zed.agents/skills/
Devin Desktop.devin/skills/
Windsurf (legacy).windsurf/skills/
OpenAI Agents SDKInstructions or sandbox Skills
HTTP / APIa request parameter
This release
Versionnot versioned
Publishedno release date on file
PriceFree
Referenceplunderstruck/data-modeling

Versions

Its author publishes no version number, so there is nothing here to pin to: what you install is the folder as it stands today. Instructions change more often than APIs do — a skill can be rewritten entirely without anything it depends on moving.

Pinning

Nothing to pin to: this skill carries no version number of its own. What you install is what the folder holds on the day you install it.

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