Skill Authoring Guide

Core Principle: Context Window is a Public Good

The context window is shared across system prompts, conversation history, skill metadata, and user requests. Challenge each piece of information:

• "Does Claude really need this explanation?"
• "Does this paragraph justify its token cost?"

Default assumption: Claude is already very smart. Only add context Claude doesn't already have. Prefer concise examples over verbose explanations.

Progressive Disclosure

Skills use three-level loading to manage context efficiently:

Level	When Loaded	Target Size	Contains
Metadata	Always in context	~100 words	name + description in frontmatter
SKILL.md body	When skill triggers	<5k words	Core instructions, workflow
Bundled resources	As needed by Claude	Unlimited	Scripts, references, assets

Implications

• Frontmatter is critical: The description field is the primary trigger mechanism
• Body is conditional: Only loaded after triggering - don't put "when to use" info here
• References defer complexity: Move detailed patterns to references/ subdirectory

Degrees of Freedom

Match instruction specificity to task fragility and variability:

Freedom	When to Use	Format
High	Multiple approaches valid, context-dependent decisions	Text-based instructions
Medium	Preferred pattern exists, some variation acceptable	Pseudocode or scripts with parameters
Low	Operations fragile/error-prone, consistency critical	Specific scripts, few parameters

Think of Claude exploring a path: a narrow bridge with cliffs needs specific guardrails (low freedom), while an open field allows many routes (high freedom).

Skill Anatomy

skill-name/
├── SKILL.md (required)
│   ├── YAML frontmatter (name + description only)
│   └── Markdown instructions
└── Optional Resources/
    ├── references/     # Documentation loaded into context as needed
    ├── scripts/        # Executable code for deterministic operations  
    └── assets/         # Files used in output (templates, icons, fonts)

Frontmatter Rules

---
name: skill-name
description: |
  What the skill does AND when to use it.
  Include trigger keywords. Be comprehensive.
  Example: "Create MCP servers for API integrations.
  Use when building tools for external services,
  implementing Model Context Protocol servers,
  or integrating APIs into agent workflows."
---

• Only name and description - No other fields
• Description is the trigger - Include all "when to use" information here
• Be specific about triggers - List contexts, keywords, and scenarios

SKILL.md Body Guidelines

• Under 500 lines - Split to references/ when approaching limit
• No "When to Use" sections - That info belongs in frontmatter description
• Progressive detail - Start with quick overview, link to references for depth
• Imperative form - Use "Create X" not "You should create X"

References Directory

For skills with multiple variants, frameworks, or detailed patterns:

cloud-deploy/
├── SKILL.md (workflow + selection guidance)
└── references/
    ├── aws.md      # AWS-specific patterns
    ├── gcp.md      # GCP-specific patterns
    └── azure.md    # Azure-specific patterns

When user chooses AWS, Claude only reads aws.md - not all variants.

Scripts Directory

Include executable scripts when:

• Same code is rewritten repeatedly
• Deterministic reliability is required
• Operations are complex but mechanical

# scripts/validate_schema.py
# Can be executed without reading into context
# Use --help pattern for black-box usage

Anti-Patterns

❌ Don't Create

• README.md, INSTALLATION_GUIDE.md, CHANGELOG.md
• User-facing documentation (skills are for agents)
• Setup/testing procedures
• Deeply nested reference structures (keep one level deep)

❌ Don't Include

• Information Claude already knows (common libraries, basic syntax)
• Redundant explanations (say it once, well)
• Verbose variable names in examples
• Unnecessary print statements in code examples

Writing Guidelines

Be Concise

❌ "In order to accomplish this task, you will need to first..."
✅ "First, create the configuration file:"

Use Tables for Structured Info

❌ "Use X for case A. Use Y for case B. Use Z for case C."
✅ | Case | Tool |
   |------|------|
   | A    | X    |
   | B    | Y    |
   | C    | Z    |

Provide Minimal Examples

❌ A 50-line example showing every possible option
✅ A 10-line example showing the core pattern

Quality Checklist

Before finalizing a skill:

• Frontmatter description covers all trigger scenarios
• SKILL.md body is under 500 lines
• No redundancy with Claude's base knowledge
• Progressive disclosure - detailed info in references/
• Degrees of freedom match task fragility
• No extra files (README, CHANGELOG, etc.)
• Examples are minimal but complete