Skill Authoring

For foundational instruction authoring principles (token economics, imperative language, formatting, anti-patterns), invoke the authoring-prompts skill first. This skill focuses on skill-specific requirements.

Create Claude Code skills that produce consistent, deterministic agent behavior. Optimize for LLM execution efficiency, not human aesthetics.

Metadata Requirements

Name Field

Requirements:

• Maximum 64 characters
• Lowercase letters, numbers, and hyphens only
• Cannot contain XML tags
• Cannot contain reserved words: "anthropic", "claude"

Naming convention: Use gerund form (verb + -ing) for clarity.

Good: processing-pdfs, analyzing-spreadsheets, writing-tests Avoid: helper, utils, tools

Description Field

Requirements:

• Maximum 1024 characters
• Must be non-empty
• Cannot contain XML tags
• Include BOTH what the skill does AND when to use it

The description determines skill invocation. Claude Code selects skills based on description relevance. Frontload invocation triggers with clear, action-oriented language.

Effective Description Structure

Pattern 1: Imperative invocation trigger first

Frontload with directive action when the skill should be invoked proactively:

# Strong - imperative trigger first
description: Use when working with .cs files, .NET projects, implementing C# features, advising on C#/.NET architecture and patterns, or answering questions about C#/.NET development. Covers async patterns, dependency injection, LINQ, and testing conventions.

# Weak - buried trigger
description: C# and .NET patterns for async, DI, LINQ, and testing. Use when working with .cs files or .NET projects.

Pattern 2: Descriptive capability with explicit triggers

For skills invoked based on context, state capabilities then enumerate clear trigger conditions:

# Strong - clear domain and triggers
description: Ruby on Rails conventions for models, controllers, routes, and testing. Use when working with Rails projects, ActiveRecord models, or Rails-specific patterns.

# Weak - vague triggers
description: Helps with Ruby on Rails development tasks.

Pattern 3: "Invoke when" for foundational skills

For skills that should be loaded before other operations, make invocation mandatory:

# Strong - explicit invocation requirement
description: Invoke this skill first when authoring any AI agent instructions. Foundational principles for writing LLM instructions (skills, CLAUDE.md, rules, commands). Covers token economics, imperative language, formatting, emphasis modifiers, and anti-patterns.

# Weak - passive suggestion
description: Foundational principles for writing instructions. Reference when creating skills or documentation.

Common Anti-Patterns

Vague scope:

• ❌ description: Helps with documents
• ✓ description: Extract text and tables from PDF files. Use when working with PDFs, forms, or document extraction.

Buried triggers:

• ❌ description: C# patterns including async and LINQ. Use when writing C# code.
• ✓ description: Use when working with .cs files or C# projects. Covers async patterns, LINQ, DI, and testing.

Generic verbs without specificity:

• ❌ description: Assists with testing activities
• ✓ description: Write xUnit tests with Moq and Bogus. Use when creating unit tests or integration tests in C#.

Multiple trigger conditions without clear enumeration:

• ❌ description: Use for various Rails tasks
• ✓ description: Use when working with Rails projects, ActiveRecord models, controllers, routes, or Rails testing.

Structure and Organization

Keep SKILL.md Concise

Target: Under 500 lines for optimal performance

When approaching this limit:

• Split content into separate reference files
• Use progressive disclosure patterns
• Move detailed reference material to bundled files

Progressive Disclosure Patterns

SKILL.md serves as an overview that points Claude to detailed materials as needed.

Pattern 1: Reference files for advanced features

## Quick start
[Basic instructions inline]

## Advanced features
**Form filling**: See [references/forms.md](references/forms.md)
**API reference**: See [references/api.md](references/api.md)

Pattern 2: Domain-specific organization

When skills cover multiple domains, organize content by domain to avoid loading irrelevant context.

skill-name/
├── SKILL.md (overview and navigation)
└── references/
    ├── domain-a.md
    ├── domain-b.md
    └── domain-c.md

Critical rules:

• Keep references one level deep from SKILL.md (no nested references)
• For reference files longer than 100 lines, include table of contents at top
• Make clear in SKILL.md when to read each reference file

Directory Structure

skill-name/
├── SKILL.md              # Required: overview and core instructions
├── scripts/              # Executable code (executed, not loaded into context)
├── references/           # Documentation (loaded as needed)
└── templates/            # Templates and examples

Content Patterns

Template Pattern

Provide templates for output format. Match strictness to requirements.

For strict requirements (API responses, data formats):

ALWAYS use this exact template structure:
[template here]

For flexible guidance:

Here is a sensible default format, adjust as needed:
[template here]

Examples Pattern

Provide concrete input/output pairs for tasks where output quality depends on seeing examples.

## Commit message format

**Example 1:**
Input: Added user authentication
Output:

feat(auth): implement JWT-based authentication

Add login endpoint and token validation

**Example 2:**
Input: Fixed date display bug
Output:

fix(reports): correct date formatting

Use UTC timestamps consistently

Include 3-5 diverse examples covering different scenarios and edge cases.

Workflow Pattern

Break complex operations into clear sequential steps. For particularly complex workflows, provide a checklist.

## Multi-step workflow

Copy this checklist and track progress:

• Step 1: Analyze input (run analyze.py)
• Step 2: Create mapping (edit config.json)
• Step 3: Validate (run validate.py)
• Step 4: Execute (run process.py)
• Step 5: Verify output

**Step 1: Analyze input**
[Detailed instructions for step 1]

**Step 2: Create mapping**
[Detailed instructions for step 2]

Feedback Loop Pattern

For quality-critical operations, implement validation cycles:

1. Perform action
2. **Validate immediately**: Run validation script
3. If validation fails:
   - Review error messages
   - Fix issues
   - Run validation again
4. **Only proceed when validation passes**
5. Continue to next step

Conditional Workflow Pattern

Guide through decision points:

1. Determine the task type:
   **Creating new?** → Follow "Creation workflow"
   **Editing existing?** → Follow "Editing workflow"

2. Creation workflow:
   [Steps for creation]

3. Editing workflow:
   [Steps for editing]

Quality Requirements

No Time-Sensitive Information

Avoid information that will become outdated.

Bad: "If doing this before August 2025, use old API"

Good: Use "old patterns" section with details/summary tags:

## Current method
[Current approach]

## Old patterns
<details>
<summary>Legacy v1 API (deprecated 2025-08)</summary>
[Historical context]
</details>

Grounding and Verification

Use techniques from prompt engineering to reduce hallucinations:

• Allow Claude to say "I don't know" explicitly
• Ask for direct quotes from documents before analysis
• Request citations for claims
• Use validation scripts for verifiable operations

Consistency Techniques

For consistent outputs:

• Specify exact output format (JSON, XML, templates)
• Provide multiple examples showing desired format
• Use prefill patterns where applicable
• Define success criteria explicitly

Executable Scripts

When including scripts in skills:

Script Purpose

Include scripts for operations requiring consistent results. Scripts are more reliable than generated code and save tokens.

Make execution intent clear:

• "Run scripts/analyze.py" (execute the script)
• "See scripts/analyze.py for the algorithm" (read as reference)

Script Quality

Scripts should:

• Handle errors explicitly, not punt to Claude
• Document all configuration values (no magic numbers)
• Use forward slashes in all paths
• List required packages explicitly

Example with clear error handling:

def process_file(path):
    """Process file, creating if missing."""
    try:
        with open(path) as f:
            return f.read()
    except FileNotFoundError:
        print(f"File {path} not found, creating default")
        with open(path, 'w') as f:
            f.write('')
        return ''

Package Dependencies

List required packages in SKILL.md. Verify they're available in the code execution environment.

Note runtime environment constraints:

• Claude API: No network access, no runtime package installation
• Claude.ai: Variable network access depending on settings

Validation Checklist

Before completing a skill, verify:

Metadata:

• Name follows conventions (lowercase-hyphens, gerund form, under 64 chars)
• Description frontloads invocation triggers, includes what AND when (under 1024 chars)

Content:

• SKILL.md body under 500 lines
• Instructions are imperative and specific
• Examples are concrete and diverse (3-5 examples)
• No time-sensitive information (or in "old patterns" section)
• Consistent terminology throughout
• No deeply nested file references (one level from SKILL.md)

Structure:

• Clear headings establish scope
• Progressive disclosure used for detailed content
• Long reference files have table of contents
• Scripts have clear execution intent
• Workflows include validation steps

Quality:

• Assumes Claude's intelligence (no obvious explanations)
• Every sentence changes agent behavior (no fluff)
• Specific constraints, not vague guidance
• Success criteria are explicit and testable

Execution:

• All file paths use forward slashes
• Required packages listed explicitly
• Error handling is explicit in scripts
• No assumptions about installed tools