# purpose-properties

This skill derives product constraints from why/how/what and flags conclusions that may have gone stale after those inputs change.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · ★ 47
- Author: haabe
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/haabe/mycelium/tree/HEAD/plugins/mycelium/skills/purpose-properties/SKILL.md
- Updated: 2026-10-24
- HTML: https://affpapa.org/en/nevibecode/skills/purpose-properties

## What it does

The skill reads `purpose.yml` and checks whether `purpose_properties` exists and whether `derived_from_hash` still matches. It distinguishes a first-time derivation from stale properties after edits to `why`, `how`, or `what`; if the hash matches, it reports the property count and stops.

For each input, it looks for a specific product choice that would contradict it. Broad quality terms such as “secure” or “fast” go through an extra screen, while rules that govern a single action are rejected as too low-level. This skill is built for the Mycelium framework. Without Mycelium, its assumed canvas state, theory gates, and harness behavior are skipped, so check that dependency before installing.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add haabe/mycelium --skill purpose-properties -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/purpose-properties/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/purpose-properties/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add haabe/mycelium --skill purpose-properties -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/purpose-properties/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add haabe/mycelium --skill purpose-properties -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/purpose-properties/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install haabe/mycelium purpose-properties
```

2. **Manually: put the files in place**
- File: `.github/skills/purpose-properties/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add haabe/mycelium --skill purpose-properties -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/haabe/mycelium --path plugins/mycelium/skills/purpose-properties
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/purpose-properties/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add haabe/mycelium --skill purpose-properties -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/haabe/mycelium/tree/HEAD/plugins/mycelium/skills/purpose-properties/SKILL.md

## When to use it
- derive product constraints from why, how, and what
- identify conclusions made stale by changes to the product definition
- separate checkable product properties from quality adjectives
- filter out rules that apply to a single action
- spot a property already covered by an existing check

## Example prompts
- Inspect `purpose.yml` and derive the product's binding properties.
- \`why` has changed; find which earlier conclusions are now stale.
- Review which properties in `purpose.yml` should be `binding`.

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: bc2da9f2b03e26c6.

BEGIN THIRD-PARTY FILE bc2da9f2b03e26c6
```text
---
name: purpose-properties
description: "Derive the binding properties your why/how/what impose on everything below them, so no solution can silently contradict your own product definition. Retrofit entry point for projects that started before v0.120.0; also the re-derive path when why/how/what change and every stance below them goes stale."
metadata:
  instruction_budget: "21"
  framework_dependency: "mycelium"
  framework_dependency_note: "This skill is designed to run within the Mycelium framework (https://github.com/haabe/mycelium). Standalone use will skip the canvas state, theory gates, and harness behavior the skill assumes. Install: /plugin install mycelium@haabe-mycelium."
---

# Purpose Properties Skill

Retrofit and re-derive entry point for `purpose.yml#purpose_properties`. **For new projects this runs
inside `/mycelium:start` Step 3b.** Use this skill when:

- The project existed before **v0.120.0** and has no `purpose_properties` (the retrofit case — every
  project created before that release, since `/mycelium:start` Step 4 exits for already-initialized
  projects and never reaches the extraction).
- `why`, `how` or `what` changed, so `derived_from_hash` no longer matches and **every stance below
  it is superseded** (the drift case — this is the one that matters most and the easiest to skip).
- A property list exists but the user wants to revisit which properties are `binding`.

Full contract: https://github.com/haabe/mycelium/blob/main/docs/purpose-stance.md (it lives in the repository, not in the installed plugin).

## Step 1: Read the current state and say which case this is

Read `purpose.yml`. Then say plainly which of these you are in, because the three have different
consequences and the user should not have to infer it:

- **No `purpose_properties`** → retrofit. Nothing below has ever been checked against the purpose.
- **Hash mismatch** → drift. Report it as *"your purpose changed after these were derived, so every
  `purpose_stance` below them was reasoned under a definition you have since changed."* This is the
  state that quietly invalidates work; name it in those terms.
- **Hash matches** → nothing to do. Report the property count and stop. Do not re-derive for tidiness.

## Step 2: Attempt extraction, and classify what fails

For every element of `why`, `how` and `what`, ask: **can I name a specific solution that would
CONTRADICT this?**

- **Yes** → candidate property. Record `property`, `verbatim` (their words, not yours), `source`, and
  the contradicting solution in `contradicted_by`.
- **No** → **do not force one.** Quality adjectives — *secure, accessible, fast, simple, delightful,
  robust* — yield nothing checkable, because every candidate solution claims to satisfy them.

**Measured 2026-08-23, blind:** *"accessible and secure"* produced **no** checkable property, while
five abstract framework principles produced clean ones. **The axis is not abstract vs concrete — it
```
END THIRD-PARTY FILE bc2da9f2b03e26c6

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First 2982 of 14253 bytes. © haabe · MIT · https://github.com/haabe/mycelium/tree/HEAD/plugins/mycelium/skills/purpose-properties/SKILL.md

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---
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