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

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 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, 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.

---
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 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. To edit an existing skill:

1. Locate the skill's 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:

---
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 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 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
• Reference implementation: See templates/SKILL.md.template for proper structure and 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 for the exact commands. Your A2 meets standards when ≥80% of test cases trigger the skill correctly.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}