create-agent-skills

SKILL.md

<essential_principles>

How Skills Work

Skills are modular, filesystem-based capabilities that provide domain expertise on demand. This skill teaches how to create effective skills.

1. Skills Are Prompts

All prompting best practices apply. Be clear, be direct, use XML structure. Assume Claude is smart - only add context Claude doesn't have.

2. SKILL.md Is Always Loaded

When a skill is invoked, Claude reads SKILL.md. Use this guarantee:

Essential principles go in SKILL.md (can't be skipped)

Workflow-specific content goes in workflows/

Reusable knowledge goes in references/

3. Router Pattern for Complex Skills
skill-name/
├── SKILL.md              # Router + principles
├── workflows/            # Step-by-step procedures (FOLLOW)
├── references/           # Domain knowledge (READ)
├── templates/            # Output structures (COPY + FILL)
└── scripts/              # Reusable code (EXECUTE)

SKILL.md asks "what do you want to do?" → routes to workflow → workflow specifies which references to read.

When to use each folder:

workflows/ - Multi-step procedures Claude follows

references/ - Domain knowledge Claude reads for context

templates/ - Consistent output structures Claude copies and fills (plans, specs, configs)

scripts/ - Executable code Claude runs as-is (deploy, setup, API calls)

4. Pure XML Structure

No markdown headings (#, ##, ###) in skill body. Use semantic XML tags:

<objective>...</objective>
<process>...</process>
<success_criteria>...</success_criteria>

Keep markdown formatting within content (bold, lists, code blocks).

5. Progressive Disclosure

SKILL.md under 500 lines. Split detailed content into reference files. Load only what's needed for the current workflow.
</essential_principles>

Create new skill

Audit/modify existing skill

Add component (workflow/reference/template/script)

Get guidance

Wait for response before proceeding.

Progressive disclosure for option 1 (create):

If user selects "Task-execution skill" → workflows/create-new-skill.md

If user selects "Domain expertise skill" → workflows/create-domain-expertise-skill.md

Progressive disclosure for option 3 (add component):

If user specifies workflow → workflows/add-workflow.md

If user specifies reference → workflows/add-reference.md

If user specifies template → workflows/add-template.md

If user specifies script → workflows/add-script.md

Intent-based routing (if user provides clear intent without selecting menu):

"audit this skill", "check skill", "review" → workflows/audit-skill.md

"verify content", "check if current" → workflows/verify-skill.md

"create domain expertise", "exhaustive knowledge base" → workflows/create-domain-expertise-skill.md

"create skill for X", "build new skill" → workflows/create-new-skill.md

"add workflow", "add reference", etc. → workflows/add-{type}.md

"upgrade to router" → workflows/upgrade-to-router.md

After reading the workflow, follow it exactly.

<quick_reference>

Skill Structure Quick Reference

Simple skill (single file):

---
name: skill-name
description: What it does and when to use it.
---

<objective>What this skill does</objective>
<quick_start>Immediate actionable guidance</quick_start>
<process>Step-by-step procedure</process>
<success_criteria>How to know it worked</success_criteria>

Complex skill (router pattern):

SKILL.md:
  <essential_principles> - Always applies
  <intake> - Question to ask
  <routing> - Maps answers to workflows

workflows/:
  <required_reading> - Which refs to load
  <process> - Steps
  <success_criteria> - Done when...

references/:
  Domain knowledge, patterns, examples

templates/:
  Output structures Claude copies and fills
  (plans, specs, configs, documents)

scripts/:
  Executable code Claude runs as-is
  (deploy, setup, API calls, data processing)

</quick_reference>

<reference_index>

Domain Knowledge

All in references/:

Structure: recommended-structure.md, skill-structure.md
Principles: core-principles.md, be-clear-and-direct.md, use-xml-tags.md
Patterns: common-patterns.md, workflows-and-validation.md
Assets: using-templates.md, using-scripts.md
Advanced: executable-code.md, api-security.md, iteration-and-testing.md
</reference_index>

<workflows_index>

Workflows

All in workflows/:

Workflow
Purpose

create-new-skill.md
Build a skill from scratch

create-domain-expertise-skill.md
Build exhaustive domain knowledge base for build/

audit-skill.md
Analyze skill against best practices

verify-skill.md
Check if content is still accurate

add-workflow.md
Add a workflow to existing skill

add-reference.md
Add a reference to existing skill

add-template.md
Add a template to existing skill

add-script.md
Add a script to existing skill

upgrade-to-router.md
Convert simple skill to router pattern

get-guidance.md
Help decide what kind of skill to build

</workflows_index>

<yaml_requirements>

YAML Frontmatter

Required fields:

---
name: skill-name          # lowercase-with-hyphens, matches directory
description: ...          # What it does AND when to use it (third person)
---

Name conventions: create-*, manage-*, setup-*, generate-*, build-*
</yaml_requirements>

<success_criteria>
A well-structured skill:

Has valid YAML frontmatter

Uses pure XML structure (no markdown headings in body)

Has essential principles inline in SKILL.md

Routes directly to appropriate workflows based on user intent

Keeps SKILL.md under 500 lines

Asks minimal clarifying questions only when truly needed

Has been tested with real usage
</success_criteria>