# skill-developer

> 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 skill activation, or implementing progressive disclosure. Covers skill structure, YAML frontmatter, trigger types (keywords, intent patterns, file paths, content patterns), enforcement levels (block, suggest, warn), hook mechanisms (UserPromptSubmit, PreToolUse), session tracking, and the 500-line rule.

- Author: Roman Gonzalez
- Repository: roman/claude-skill-activation.nix
- Version: 20260120124039
- Stars: 1
- Forks: 0
- Last Updated: 2026-02-06
- Source: https://github.com/roman/claude-skill-activation.nix
- Web: https://mule.run/skillshub/@@roman/claude-skill-activation.nix~skill-developer:20260120124039

---

---
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 skill activation, or implementing progressive disclosure. Covers skill structure, YAML frontmatter, trigger types (keywords, intent patterns, file paths, content patterns), enforcement levels (block, suggest, warn), hook mechanisms (UserPromptSubmit, PreToolUse), session tracking, and the 500-line rule.
---

# 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

### Architecture

**1. UserPromptSubmit Hook** (Proactive Suggestions)
- **Program**: `claude-skill-activation`
- **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

### Configuration File

**Location**: The skill-rules.json path is determined by:
1. **Check UserPromptSubmit hook** in `.claude/settings.json` for file path parameter
2. **Default fallback**: `$CLAUDE_PROJECT_DIR/.claude/skills/skill-rules.json`

**How to find your path:**
- Read `.claude/settings.json` → `hooks.UserPromptSubmit[].command`
- Look for the file path argument to `claude-skill-activation`
- Example: `/path/to/claude-skill-activation ~/.claude/skill-rules.json`
  → Your path is `~/.claude/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.

⚠️ **CRITICAL**: The skill-rules.json file MUST have top-level `version` and `skills` fields!

**Complete File Template (for NEW file):**
```json
{
  "version": "1.0",
  "skills": {
    "my-new-skill": {
      "type": "domain",
      "enforcement": "suggest",
      "priority": "medium",
      "promptTriggers": {
        "keywords": ["keyword1", "keyword2"],
        "intentPatterns": ["(create|add).*?something"]
      }
    }
  }
}
```

**Adding to Existing File:**
If skill-rules.json already exists with other skills, add your new skill inside the `skills` object:
```json
{
  "version": "1.0",
  "skills": {
    "existing-skill": { ... },
    "my-new-skill": {       ← Add here
      "type": "domain",
      "enforcement": "suggest",
      "priority": "medium",
      "promptTriggers": {
        "keywords": ["keyword1", "keyword2"],
        "intentPatterns": ["(create|add).*?something"]
      }
    }
  }
}
```

### Step 3: Test Triggers

```bash
# Auto-detects configuration and tests skill activation
test-skill-activation "your test prompt"

# With custom session ID
test-skill-activation -s custom-session "your test prompt"
```

### 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 500 lines
- ✅ Use progressive disclosure with reference files
- ✅ Add table of contents to reference files > 100 lines
- ✅ Write detailed description with trigger keywords
- ✅ Test with 3+ real scenarios before documenting
- ✅ Iterate based on actual usage

---

## Adding Existing Skill to skill-rules.json

If you already have a skill file (SKILL.md) and want to add triggers for it:

### Step 1: Find your skill-rules.json path

See [Configuration File](#configuration-file) section above for path discovery instructions.

### Step 2: Read existing skill-rules.json (if any)

```bash
cat ~/.claude/skill-rules.json  # Use your actual path from Step 1
```

### Step 3: Add skill entry

Use the JSON templates from [Quick Start Step 2](#step-2-add-to-skill-rulesjson) above:
- For NEW/EMPTY file → Use "Complete File Template"
- For EXISTING file → Use "Adding to Existing File" template

### Step 4: Test the triggers

```bash
test-skill-activation "your test prompt"
```

---

## Enforcement Levels

### BLOCK (Critical Guardrails)

- Physically prevents Edit/Write tool execution
- Exit code 2 from hook, stderr → Claude
- Claude sees message and must use skill to proceed
- **Use For**: Critical mistakes, data integrity, security issues

**Example:** Database column name verification

### SUGGEST (Recommended)

- Reminder injected before Claude sees prompt
- Claude is aware of relevant skills
- Not enforced, just advisory
- **Use For**: Domain guidance, best practices, how-to guides

**Example:** Frontend development guidelines

### WARN (Optional)

- Low priority suggestions
- Advisory only, minimal enforcement
- **Use For**: Nice-to-have suggestions, informational reminders

**Rarely used** - most skills are either BLOCK or SUGGEST.

---

## Skip Conditions & User Control

### 1. Session Tracking

**Purpose:** Don't nag repeatedly in same session

**How it works:**
- First edit → Hook blocks, updates session state
- Second edit (same session) → Hook allows
- Different session → Blocks again

**State File:** `.claude/hooks/state/skills-used-{session_id}.json`

---

## Testing Checklist

When creating a new skill, verify:

- [ ] Skill file created in `.claude/skills/{name}/SKILL.md`
- [ ] Proper frontmatter with name and description
- [ ] Entry added to `skill-rules.json`
- [ ] Keywords tested with real prompts
- [ ] Intent patterns tested with variations
- [ ] File path patterns tested with actual files
- [ ] Content patterns tested against file contents
- [ ] Block message is clear and actionable (if guardrail)
- [ ] Skip conditions configured appropriately
- [ ] Priority level matches importance
- [ ] No false positives in testing
- [ ] No false negatives in testing
- [ ] Performance is acceptable (<100ms or <200ms)
- [ ] JSON syntax validated: `jq . skill-rules.json`
- [ ] **SKILL.md under 500 lines** ⭐
- [ ] Reference files created if needed
- [ ] Table of contents added to files > 100 lines

---

## Reference Files

For detailed information on specific topics, see in the `references` folder:

### [TRIGGER_TYPES.md](TRIGGER_TYPES.md)
Complete guide to all trigger types:
- Keyword triggers (explicit topic matching)
- Intent patterns (implicit action detection)
- File path triggers (glob patterns)
- Content patterns (regex in files)
- Best practices and examples for each
- Common pitfalls and testing strategies

### [SKILL_RULES_REFERENCE.md](SKILL_RULES_REFERENCE.md)
Complete skill-rules.json schema:
- Full TypeScript interface definitions
- Field-by-field explanations
- Complete guardrail skill example
- Complete domain skill example
- Validation guide and common errors

### [HOOK_MECHANISMS.md](HOOK_MECHANISMS.md)
Deep dive into hook internals:
- UserPromptSubmit flow (detailed)
- PreToolUse flow (detailed)
- Exit code behavior table (CRITICAL)
- Session state management
- Performance considerations

### [TROUBLESHOOTING.md](TROUBLESHOOTING.md)
Comprehensive debugging guide:
- Skill not triggering (UserPromptSubmit)
- PreToolUse not blocking
- False positives (too many triggers)
- Hook not executing at all
- Performance issues

### [PATTERNS_LIBRARY.md](PATTERNS_LIBRARY.md)
Ready-to-use pattern collection:
- Intent pattern library (regex)
- File path pattern library (glob)
- Content pattern library (regex)
- Organized by use case
- Copy-paste ready

### [ADVANCED.md](ADVANCED.md)
Future enhancements and ideas:
- Dynamic rule updates
- Skill dependencies
- Conditional enforcement
- Skill analytics
- Skill versioning

---

## Quick Reference Summary

### Create New Skill (5 Steps)

1. Create `.claude/skills/{name}/SKILL.md` with frontmatter
2. Add entry to skill-rules.json (⚠️ MUST have `version` + `skills` wrapper!)
3. Test with hook command
4. Refine patterns based on testing
5. Keep SKILL.md under 500 lines

### Add Existing Skill to skill-rules.json (4 Steps)

1. Find your skill-rules.json path from `.claude/settings.json` hook command
2. Read existing file (if any) to see current structure
3. Add skill entry to `skills` object (⚠️ MUST have `version` + `skills` wrapper!)
4. Test with hook command: `echo '{"session_id":"test","prompt":"..."}' | $HOOK_CMD`

### Trigger Types

- **Keywords**: Explicit topic mentions
- **Intent**: Implicit action detection
- **File Paths**: Location-based activation
- **Content**: Technology-specific detection

See [TRIGGER_TYPES.md](TRIGGER_TYPES.md) for complete details.

### Enforcement

- **BLOCK**: Exit code 2, critical only
- **SUGGEST**: Inject context, most common
- **WARN**: Advisory, rarely used

### Anthropic Best Practices

✅ **500-line rule**: Keep SKILL.md under 500 lines
✅ **Progressive disclosure**: Use reference files for details
✅ **Table of contents**: Add to reference files > 100 lines
✅ **One level deep**: Don't nest references deeply
✅ **Rich descriptions**: Include all trigger keywords (max 1024 chars)
✅ **Test first**: Build 3+ evaluations before extensive documentation
✅ **Gerund naming**: Prefer verb + -ing (e.g., "processing-pdfs")

### Troubleshoot

```bash
test-skill-activation "your test prompt"
```

See [TROUBLESHOOTING.md](TROUBLESHOOTING.md) for complete debugging guide.

---

## Related Files

**Configuration:**
- `skill-rules.json` - Master configuration (path determined by hook command in settings.json)
- `.claude/hooks/state/` - Session tracking
- `.claude/settings.json` - Hook registration (check here for skill-rules.json path)

**Hooks:**
- Hook command in settings.json (e.g., `claude-skill-activation <path>`) - UserPromptSubmit

**All Skills:**
- `.claude/skills/*/SKILL.md` - Skill content files

---

**Skill Status**: COMPLETE - Restructured following Anthropic best practices ✅
**Line Count**: < 500 (following 500-line rule) ✅
**Progressive Disclosure**: Reference files for detailed information ✅

**Next**: Create more skills, refine patterns based on usage