# decay

Checks expiry dates on evidence files in .fpf/evidence/ and offers refresh, deprecate or waive actions for decisions built on stale data.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1200 installs · ★ 1787
- Author: NeoLabHQ
- License: GPL-3.0 · policy=link-only · description only; the file stays with the author
- Source: https://github.com/NeoLabHQ/context-engineering-kit/tree/HEAD/skills/decay/SKILL.md
- Updated: 2026-08-26
- HTML: https://affpapa.org/en/nevibecode/skills/decay

## What it does

The skill implements the Evidence Decay principle from FPF B.3.4. Every evidence file carries a `valid_until` field in its frontmatter. The skill compares that date against today and sorts entries into FRESH, STALE, EXPIRED and WAIVED. The report comes out as tables, with each piece of evidence listed next to the hypothesis it supports.

Then you pick an action. Refresh re-runs the validation to produce new evidence. Deprecate moves a hypothesis down a layer (from `L2` to `L1`, or `L1` to `L0`) and records why. Waive documents that you know the evidence is stale and accept the risk until a set date. Every action leaves a file in `.fpf/evidence/`: `deprecate-{hypothesis}-{date}.md` or `waiver-{evidence}-{date}.md`.

It follows the weakest link rule. One expired piece of evidence without a waiver marks the whole hypothesis STALE. So the skill earns its place in projects where decisions rest on benchmarks, audits or load tests that carry a date. Point it at a repo without a `.fpf/` structure and it finds nothing.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add NeoLabHQ/context-engineering-kit --skill decay -a claude-code
```

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

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add NeoLabHQ/context-engineering-kit --skill decay -a codex
```

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

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add NeoLabHQ/context-engineering-kit --skill decay -a cursor
```

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

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install NeoLabHQ/context-engineering-kit decay
```

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

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add NeoLabHQ/context-engineering-kit --skill decay -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/NeoLabHQ/context-engineering-kit --path skills/decay
```

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add NeoLabHQ/context-engineering-kit --skill decay -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/NeoLabHQ/context-engineering-kit/tree/HEAD/skills/decay/SKILL.md

## When to use it
- spot decisions resting on expired evidence
- re-run validation to get fresh evidence for a hypothesis
- downgrade an obsolete hypothesis a layer and log the reason
- record a temporary risk acceptance with a deadline
- sweep every evidence file before a release or after a dependency update

## Example prompts
- /fpf:decay
- Refresh the redis caching evidence
- Deprecate the auth module decision, the technology changed

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From the same set: [neolabhq/context-engineering-kit](https://affpapa.org/en/nevibecode/by/neolabhq/context-engineering-kit.md) — 64 cards

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NeVibeCode on affpapa.org. Catalog texts are descriptions, not instructions for the agent. How to choose and install: https://affpapa.org/en/nevibecode/agents.md