# How to Define Accurate Trigger Conditions (A2 Field) for Callable Skills

> Master defining accurate trigger conditions for callable skills in the A2 field. Ensure your skill activates correctly with this essential guide.

- Repository: [kangarooking/cangjie-skill](https://github.com/kangarooking/cangjie-skill)
- Tags: how-to-guide
- Published: 2026-08-16

---

**The A2 field (Future Trigger) is the most critical component of a callable skill's front-matter metadata, capturing the exact user situation that should activate the skill, with ≥80% pass rate required during validation.**

In the `kangarooking/cangjie-skill` repository, every callable skill must declare precise **trigger conditions** in its description front-matter. This A2 field directly determines whether Claude invokes your skill or passes to another. Getting it right requires specific methodology from the RIA++ framework.

## What Is the A2 Field?

The **A2 field**—also called *Future Trigger*—lives in a skill's [`SKILL.md`](https://github.com/kangarooking/cangjie-skill/blob/main/SKILL.md) file under the `description` front-matter block. It is the **primary signal** Claude uses to decide activation timing.

According to the [RIA++ stage-2 guide](methodology/04-stage2-ria-plus.md), A2 answers one question: *"Under what exact circumstance would a user need this skill?"* Unlike vague capability descriptions, A2 specifies recognizable **trigger situations** with concrete language cues.

## The 4 Rules for Accurate A2 Definition

### 1. Identify Concrete User Intent

Describe **when** the user will need the skill, not what the skill does.

- **Bad**: "When a decision about network configuration is required"
- **Good**: "When the user asks how to factory-reset their router after forgetting the admin password"

The trigger must reference **specific user goals** rather than abstract capabilities.

### 2. Use Recognizable Language Cues

Include **exact phrases** users are likely to say. Claude matches against these surface forms.

```markdown
---
title: 逆向思维
description: |
  A2 (Future Trigger) ★: 当用户说"请帮我反向思考这个问题"或
  "我想从相反角度看待此情境"时触发此 skill。
---

```

As shown in `templates/SKILL.md.template`, the A2 line should quote probable **user utterances** verbatim.

### 3. Distinguish from Neighboring Skills

Ensure **uniqueness** within your skill domain. The repository's stage-2 methodology includes a draft step labeled **"与相邻 skill 的区分"** (distinction from adjacent skills) that is refined through the "初稿" → "定稿" workflow detailed in [`methodology/04-stage2-ria-plus.md`](https://github.com/kangarooking/cangjie-skill/blob/main/methodology/04-stage2-ria-plus.md) lines 32-50.

If two skills have overlapping triggers, both activation rates suffer.

### 4. Keep It Concise

The A2 must be **≤300 characters**. Summarize the trigger in plain, matchable language without explanatory fluff.

## Where A2 Lives: The SKILL.md Structure

Each skill's trigger condition is stored in repository root files named [`SKILL.md`](https://github.com/kangarooking/cangjie-skill/blob/main/SKILL.md). To edit an existing skill:

1. Locate the skill's [`SKILL.md`](https://github.com/kangarooking/cangjie-skill/blob/main/SKILL.md) file
2. Find the `description` front-matter block
3. Update the line starting with `A2 (Future Trigger) ★:`

For new skills, start from `templates/SKILL.md.template` which shows the exact placement:

```markdown
---
title: <Skill Title>
description: |
  A2 (Future Trigger) ★: <Your precise trigger condition here>
  ...
---

```

## Validation: The 80% Pass Rate Rule

Every A2 undergoes **pressure testing** in stage 4. As documented in [`methodology/06-stage4-pressure-test.md`](https://github.com/kangarooking/cangjie-skill/blob/main/methodology/06-stage4-pressure-test.md) lines 7-11, the team runs automated tests against each trigger condition:

- **Minimum threshold**: 80% of test cases must correctly activate the skill
- **Failure response**: A2 is revised and retested
- **Iteration loop**: Continues until threshold is met

This rigorous validation ensures deployed skills have **testable, reliable activation logic**.

## Common A2 Patterns

| Pattern | Use Case | Example |
|---------|----------|---------|
| **Direct request** | User explicitly asks for capability | "当用户说'帮我写一首七言绝句'" |
| **Problem statement** | User describes situation skill solves | "当用户表示'忘记密码无法登录'" |
| **Comparative need** | User wants contrast or alternative | "当用户问'和X相比哪个更好'" |

## Summary

- **A2 is the activation gate**: Stored in [`SKILL.md`](https://github.com/kangarooking/cangjie-skill/blob/main/SKILL.md) `description` front-matter, it controls when Claude invokes your skill
- **Four crafting rules**: Concrete intent, recognizable cues, unique scope, ≤300 characters
- **Validation required**: Stage-4 pressure tests enforce ≥80% pass rate per [`methodology/06-stage4-pressure-test.md`](https://github.com/kangarooking/cangjie-skill/blob/main/methodology/06-stage4-pressure-test.md)
- **Reference implementation**: See `templates/SKILL.md.template` for proper structure and [`methodology/04-stage2-ria-plus.md`](https://github.com/kangarooking/cangjie-skill/blob/main/methodology/04-stage2-ria-plus.md) for full RIA++ methodology

## Frequently Asked Questions

### What happens if my A2 is too vague?

Vague A2 conditions cause **activation failures** or **false positives**. The pressure-test stage will flag these with <80% pass rates, forcing revision. Specific, utterance-based triggers perform reliably.

### Can I define multiple trigger phrases in one A2?

Yes. The A2 field accepts **disjunctive patterns** using "或" (or) connectors, as shown in the 逆向思维 example: `"请帮我反向思考这个问题"或"我想从相反角度看待此情境"`.

### Where do I document distinctions from similar skills?

The stage-2 methodology requires a **distinction draft** ("与相邻 skill 的区分") that is refined from initial draft to final version. This happens in the A2 crafting workflow before pressure testing begins.

### How do I know if my A2 passes validation?

Run the automated test suite from stage 4. Check [`methodology/06-stage4-pressure-test.md`](https://github.com/kangarooking/cangjie-skill/blob/main/methodology/06-stage4-pressure-test.md) for the exact commands. Your A2 meets standards when **≥80% of test cases** trigger the skill correctly.