# distill

Reads an existing codebase and pulls out a behavioural specification in Allium. Useful when you need to document what a system does at the domain level.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 2600 installs · ★ 521
- Author: juxt
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/juxt/allium/tree/HEAD/skills/distill/SKILL.md
- Updated: 2026-09-27
- HTML: https://affpapa.org/en/nevibecode/skills/distill

## What it does

The skill walks through code and separates domain decisions from implementation detail. Code tells you how something works; a spec captures what it does and why it matters. Two questions do the filtering: why would a stakeholder care, and could this be built differently while staying the same system. A yes to the second sends the detail back to implementation, a no puts it in the spec.

It runs in two modes. Interactive means it asks you in the conversation and waits. Non-interactive means it runs as the `distill` subagent, for instance inside the Allium loop, where no user is reachable — then judgement calls like intended versus accidental behaviour, actor identity or candidate processes get recorded as `open question` declarations in the spec and listed in the final output.

Before touching code, the skill settles scope: which subset of the codebase you are specifying, what to exclude (legacy, infrastructure, deprecated paths, features behind flags), who owns the spec. It documents included and excluded items at the top of the `.allium` file and puts the language version marker on the first line. In a monorepo holding several systems, skipping that step drags other teams' domains into your spec.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add juxt/allium --skill distill -a claude-code
```

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

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add juxt/allium --skill distill -a codex
```

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

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add juxt/allium --skill distill -a cursor
```

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

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install juxt/allium distill
```

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

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add juxt/allium --skill distill -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/juxt/allium --path skills/distill
```

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add juxt/allium --skill distill -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/juxt/allium/tree/HEAD/skills/distill/SKILL.md

## When to use it
- reverse engineer a spec from an existing implementation
- separate domain decisions from implementation details
- draw spec boundaries in a monorepo
- park unconfirmed judgement calls as open questions
- document what a codebase does in Allium terms

## Example prompts
- Extract an Allium spec from the interview scheduling service, exclude auth and analytics
- Run distill over this repo and record ambiguous decisions as open questions
- Generate a behavioural spec for the orders module, leave the legacy V1 API alone

## Source text · SKILL.md · MIT

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BEGIN THIRD-PARTY FILE 1103f1e3d45c2bb1
```text
---
name: distill
description: "Extract an Allium specification from an existing codebase. Use when the user has existing code and wants to distil behaviour into a spec, reverse engineer a specification from implementation, generate a spec from code, turn implementation into a behavioural specification, or document what a codebase does in Allium terms."
---

# Distillation guide

This guide covers extracting Allium specifications from existing codebases. The core challenge is the same as forward elicitation: finding the right level of abstraction. In elicitation you filter out implementation ideas as they arise. In distillation you filter out implementation details that already exist. Both require the same judgement about what matters at the domain level.

Code tells you *how* something works. A specification captures *what* it does and *why* it matters. The skill is asking "why does the stakeholder care about this?" and "could this be different while still being the same system?"

## Interaction modes

This skill runs in two modes. Every instruction below that asks, prompts or validates with the user follows the mode:

- **Interactive** — running inline in a conversation. Ask the user directly and wait for the answer.
- **Non-interactive** — running as the `distill` subagent (for example inside the Allium loop), where no user is reachable. Scope the distillation from the goal you were given, and do not guess at judgement calls: record each unconfirmed judgement — intended vs accidental behaviour, actor identity, candidate processes, scope exclusions — as an `open question` declaration in the distilled spec, and list the parked questions in your final output.

## Scoping the distillation effort

Before diving into code, establish what you are trying to specify. Not every line of code deserves a place in the spec.

### Questions to ask first

1. **"What subset of this codebase are we specifying?"**
   Mono repos often contain multiple distinct systems. You may only need a spec for one service or domain. Clarify boundaries explicitly before starting.

2. **"Is there code we should deliberately exclude?"**
   - **Legacy code**: features kept for backwards compatibility but not part of the core system
   - **Incidental code**: supporting infrastructure that is not domain-level (logging, metrics, deployment)
   - **Deprecated paths**: code scheduled for removal
   - **Experimental features**: behind feature flags, not yet design decisions

3. **"Who owns this spec?"**
   Different teams may own different parts of a mono repo. Each team's spec should focus on their domain.

### The "Would we rebuild this?" test
```
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First 2661 of 33257 bytes. © juxt · MIT · https://github.com/juxt/allium/tree/HEAD/skills/distill/SKILL.md

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