Skill Developer

---
name: skill-developer
description: Create and manage Claude Code skills following Anthropic best practices. Use when creating new skills, modifying skill-rules.json, understanding trigger patterns, working with hooks, debugging skil...
category: AI & Agents
source: antigravity
tags: [typescript, react, node, pdf, markdown, claude, ai, workflow, template, document]
url: https://github.com/sickn33/antigravity-awesome-skills/tree/main/skills/skill-developer
---


# Skill Developer Guide

## Purpose

Comprehensive guide for creating and managing skills in Claude Code with auto-activation system, following Anthropic's official best practices including the 500-line rule and progressive disclosure pattern.

## When to Use This Skill

Automatically activates when you mention:
- Creating or adding skills
- Modifying skill triggers or rules
- Understanding how skill activation works
- Debugging skill activation issues
- Working with skill-rules.json
- Hook system mechanics
- Claude Code best practices
- Progressive disclosure
- YAML frontmatter
- 500-line rule

---

## System Overview

### Two-Hook Architecture

**1. UserPromptSubmit Hook** (Proactive Suggestions)
- **File**: `.claude/hooks/skill-activation-prompt.ts`
- **Trigger**: BEFORE Claude sees user's prompt
- **Purpose**: Suggest relevant skills based on keywords + intent patterns
- **Method**: Injects formatted reminder as context (stdout → Claude's input)
- **Use Cases**: Topic-based skills, implicit work detection

**2. Stop Hook - Error Handling Reminder** (Gentle Reminders)
- **File**: `.claude/hooks/error-handling-reminder.ts`
- **Trigger**: AFTER Claude finishes responding
- **Purpose**: Gentle reminder to self-assess error handling in code written
- **Method**: Analyzes edited files for risky patterns, displays reminder if needed
- **Use Cases**: Error handling awareness without blocking friction

**Philosophy Change (2025-10-27):** We moved away from blocking PreToolUse for Sentry/error handling. Instead, use gentle post-response reminders that don't block workflow but maintain code quality awareness.

### Configuration File

**Location**: `.claude/skills/skill-rules.json`

Defines:
- All skills and their trigger conditions
- Enforcement levels (block, suggest, warn)
- File path patterns (glob)
- Content detection patterns (regex)
- Skip conditions (session tracking, file markers, env vars)

---

## Skill Types

### 1. Guardrail Skills

**Purpose:** Enforce critical best practices that prevent errors

**Characteristics:**
- Type: `"guardrail"`
- Enforcement: `"block"`
- Priority: `"critical"` or `"high"`
- Block file edits until skill used
- Prevent common mistakes (column names, critical errors)
- Session-aware (don't repeat nag in same session)

**Examples:**
- `database-verification` - Verify table/column names before Prisma queries
- `frontend-dev-guidelines` - Enforce React/TypeScript patterns

**When to Use:**
- Mistakes that cause runtime errors
- Data integrity concerns
- Critical compatibility issues

### 2. Domain Skills

**Purpose:** Provide comprehensive guidance for specific areas

**Characteristics:**
- Type: `"domain"`
- Enforcement: `"suggest"`
- Priority: `"high"` or `"medium"`
- Advisory, not mandatory
- Topic or domain-specific
- Comprehensive documentation

**Examples:**
- `backend-dev-guidelines` - Node.js/Express/TypeScript patterns
- `frontend-dev-guidelines` - React/TypeScript best practices
- `error-tracking` - Sentry integration guidance

**When to Use:**
- Complex systems requiring deep knowledge
- Best practices documentation
- Architectural patterns
- How-to guides

---

## Quick Start: Creating a New Skill

### Step 1: Create Skill File

**Location:** `.claude/skills/{skill-name}/SKILL.md`

**Template:**
```markdown
---
name: my-new-skill
description: Brief description including keywords that trigger this skill. Mention topics, file types, and use cases. Be explicit about trigger terms.
---

# My New Skill

## Purpose
What this skill helps with

## When to Use
Specific scenarios and conditions

## Key Information
The actual guidance, documentation, patterns, examples
```

**Best Practices:**
- ✅ **Name**: Lowercase, hyphens, gerund form (verb + -ing) preferred
- ✅ **Description**: Include ALL trigger keywords/phrases (max 1024 chars)
- ✅ **Content**: Under 500 lines - use reference files for details
- ✅ **Examples**: Real code examples
- ✅ **Structure**: Clear headings, lists, code blocks

### Step 2: Add to skill-rules.json

See [SKILL_RULES_REFERENCE.md](SKILL_RULES_REFERENCE.md) for complete schema.

**Basic Template:**
```json
{
  "my-new-skill": {
    "type": "domain",
    "enforcement": "suggest",
    "priority": "medium",
    "promptTriggers": {
      "keywords": ["keyword1", "keyword2"],
      "intentPatterns": ["(create|add).*?something"]
    }
  }
}
```

### Step 3: Test Triggers

**Test UserPromptSubmit:**
```bash
echo '{"session_id":"test","prompt":"your test prompt"}' | \
  npx tsx .claude/hooks/skill-activation-prompt.ts
```

**Test PreToolUse:**
```bash
cat <<'EOF' | npx tsx .claude/hooks/skill-verification-guard.ts
{"session_id":"test","tool_name":"Edit","tool_input":{"file_path":"test.ts"}}
EOF
```

### Step 4: Refine Patterns

Based on testing:
- Add missing keywords
- Refine intent patterns to reduce false positives
- Adjust file path patterns
- Test content patterns against actual files

### Step 5: Follow Anthropic Best Practices

✅ Keep SKILL.md under 50