allium

A formal language for describing software behaviour in terms of what users or systems can observe, without specifying how the software is built. It can generate integration and end-to-end tests, which check complete interactions across system parts.

In plain words
What is it for?
Use it to write or read .allium specifications, define domain rules, and create integration or end-to-end tests from those specifications.
Why use it?
It exposes unclear requirements before implementation and keeps behaviour specifications independent of programming languages, frameworks, databases, and user-interface designs.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/juxt/claude-plugins/allium
Any agent
npx skills add juxt/claude-plugins --skill allium
Clone the repo
git clone --depth 1 https://github.com/juxt/claude-plugins

Made for: Claude Code, Codex.

Per session 18 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,775 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 100% copy Near-identical to another mod in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00018 $0.03775
Opus 5 $0.00009 $0.01887
Sonnet 5 $0.00004 $0.00755
Haiku 4.5 $0.00002 $0.00378

Measured 2d ago against content hash bad4431c65c9, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

allium scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

This is a copy

100% identical to allium — 0 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

plugins/allium/skills/allium/SKILL.md · 342 lines

How it starts

The opening of the file, as written. The whole thing — 342 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Allium

Allium is a formal language for capturing software behaviour at the domain level. It sits between informal feature descriptions and implementation, providing a precise way to specify what software does without prescribing how it's built.

The name comes from the botanical family containing onions and shallots, continuing a tradition in behaviour specification tooling established by Cucumber and Gherkin.

Key principles:

  • Describes observable behaviour, not implementation
  • Captures domain logic that matters at the behavioural level
  • Generates integration and end-to-end tests (not unit tests)
  • Forces ambiguities into the open before implementation
  • Implementation-agnostic: the same spec could be implemented in any language

Allium does NOT specify programming language or framework choices, database schemas or storage mechanisms, API designs or UI layouts, or internal algorithms (unless they are domain-level concerns).

Routing table

Task Tool When
Writing or reading .allium files this skill You need language syntax and structure
Building a spec through conversation elicit skill User describes a feature or behaviour they want to build
Extracting a spec from existing code distill skill User has implementation code and wants a spec from it
Modifying an existing spec tend skill User wants targeted changes to .allium files
Checking spec-to-code alignment weed skill User wants to find or fix divergences between spec and implementation
Generating tests from a spec propagate skill User wants to generate tests, PBT properties or state machine tests from a specification
Attesting a loop's convergence witness skill User wants to independently confirm a run's convergence claim from ground truth — tests really pass, no generated test was weakened, no blocking question was silently parked
Driving the whole loop to convergence this skill (see driving the loop) User wants to build or reconcile a feature end to end — /allium <goal> runs the gather→act→verify→repeat loop autonomously until spec, tests and code agree

Read the full file on GitHub · 342 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 342 lines · 18 tokens per session scan A bad4431c65c9

Subscribe to this mod's changes

allium is a skill published in the GitHub repository juxt/claude-plugins (10 stars, last pushed 4d ago), licensed MIT. It adds 18 tokens to every session and 3,775 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to allium, differing in 0 lines, and is treated as a copy.

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