Guide for creating effective skills. This command should be used when users want to create a new skill (or update an existing skill) that extends Claude's capabilities with specialized knowledge, workflows, or tool integrations. Use when creating new skills, editing existing skills, or verifying skills work before deployment - applies TDD to process documentation by testing with subagents before writing, iterating until bulletproof against rationalization
Guide for creating effective skills. This command should be used when users want to create a new skill (or update an existing skill) that extends Claude's capabilities with specialized knowledge, workflows, or tool integrations. Use when creating new skills, editing existing skills, or verifying skills work before deployment - applies TDD to process documentation by testing with subagents before writing, iterating until bulletproof against rationalization
Create Skill Command
This command provides guidance for creating effective skills.
Overview
Writing skills IS Test-Driven Development applied to process documentation.
Personal skills live in agent-specific directories (~/.claude/skills for Claude Code, ~/.codex/skills for Codex)
You write test cases (pressure scenarios with subagents), watch them fail (baseline behavior), write the skill (documentation), watch tests pass (agents comply), and refactor (close loopholes).
Core principle: If you didn't watch an agent fail without the skill, you don't know if the skill teaches the right thing.
REQUIRED BACKGROUND: You MUST understand Test-Driven Development before using this skill. That skill defines the fundamental RED-GREEN-REFACTOR cycle. This skill adapts TDD to documentation.
Official guidance: The Anthropic's official skill authoring best practices provided at the /customaize-agent:apply-anthropic-skill-best-practices command, they enhance customize-agent:prompt-engineering skill. Use skill and the document, as they not copy but add to each other. These document provides additional patterns and guidelines that complement the TDD-focused approach in this skill.
About Skills
Skills are modular, self-contained packages that extend Claude's capabilities by providing
specialized knowledge, workflows, and tools. Think of them as "onboarding guides" for specific
domains or tasks—they transform Claude from a general-purpose agent into a specialized agent
equipped with procedural knowledge that no model can fully possess.
```markdown
Write code before test? Delete it.
```
```markdown
Write code before test? Delete it. Start over.
What is a Skill?
A skill is a reference guide for proven techniques, patterns, or tools. Skills help future Claude instances find and apply effective approaches.
Skills are NOT: Narratives about how you solved a problem once
What Skills Provide
Specialized workflows - Multi-step procedures for specific domains
Tool integrations - Instructions for working with specific file formats or APIs
Domain expertise - Company-specific knowledge, schemas, business logic
Bundled resources - Scripts, references, and assets for complex and repetitive tasks
TDD Mapping for Skills
TDD Concept
Skill Creation
Test case
Pressure scenario with subagent
Production code
Skill document (SKILL.md)
Test fails (RED)
Agent violates rule without skill (baseline)
Test passes (GREEN)
Agent complies with skill present
Refactor
Close loopholes while maintaining compliance
Write test first
Run baseline scenario BEFORE writing skill
Watch it fail
Document exact rationalizations agent uses
Minimal code
Write skill addressing those specific violations
Watch it pass
Verify agent now complies
Refactor cycle
Find new rationalizations → plug → re-verify
The entire skill creation process follows RED-GREEN-REFACTOR.
When to Create a Skill
Create when:
Technique wasn't intuitively obvious to you
You'd reference this again across projects
Pattern applies broadly (not project-specific)
Others would benefit
Don't create for:
One-off solutions
Standard practices well-documented elsewhere
Project-specific conventions (put in CLAUDE.md)
Skill Types
Technique
Concrete method with steps to follow (condition-based-waiting, root-cause-tracing)
Pattern
Way of thinking about problems (flatten-with-flags, test-invariants)
Reference
API docs, syntax guides, tool documentation (office docs)
Directory Structure
skills/
skill-name/
SKILL.md # Main reference (required)
supporting-file.* # Only if needed
Flat namespace - all skills in one searchable namespace
Separate files for:
Heavy reference (100+ lines) - API docs, comprehensive syntax
Reusable tools - Scripts, utilities, templates
Keep inline:
Principles and concepts
Code patterns (< 50 lines)
Everything else
Anatomy of a Skill
Every skill consists of a required SKILL.md file and optional bundled resources:
skill-name/
├── SKILL.md (required)
│ ├── YAML frontmatter metadata (required)
│ │ ├── name: (required)
│ │ └── description: (required)
│ └── Markdown instructions (required)
└── Bundled Resources (optional)
├── scripts/ - Executable code (Python/Bash/etc.)
├── references/ - Documentation intended to be loaded into context as needed
└── assets/ - Files used in output (templates, icons, fonts, etc.)
SKILL.md (required)
Metadata Quality: The name and description in YAML frontmatter determine when Claude will use the skill. Be specific about what the skill does and when to use it. Use the third-person (e.g. "This skill should be used when..." instead of "Use this skill when...").
SKILL.md Structure
Frontmatter (YAML):
Only two fields supported: name and description
Max 1024 characters total
name: Use letters, numbers, and hyphens only (no parentheses, special chars)
description: Third-person, includes BOTH what it does AND when to use it
Start with "Use when..." to focus on triggering conditions
Include specific symptoms, situations, and contexts
Keep under 500 characters if possible
---
name: Skill-Name-With-Hyphens
description: Use when [specific triggering conditions and symptoms] - [what the skill does and how it helps, written in third person]
---# Skill Name## Overview
What is this? Core principle in 1-2 sentences.
## When to Use
[Small inline flowchart IF decision non-obvious]
Bullet list with SYMPTOMS and use cases
When NOT to use
## Core Pattern (for techniques/patterns)
Before/after code comparison
## Quick Reference
Table or bullets for scanning common operations
## Implementation
Inline code for simple patterns
Link to file for heavy reference or reusable tools
## Common Mistakes
What goes wrong + fixes
## Real-World Impact (optional)
Concrete results
Bundled Resources (optional)
Scripts (scripts/)
Executable code (Python/Bash/etc.) for tasks that require deterministic reliability or are repeatedly rewritten.
When to include: When the same code is being rewritten repeatedly or deterministic reliability is needed
Example: scripts/rotate_pdf.py for PDF rotation tasks
Benefits: Token efficient, deterministic, may be executed without loading into context
Note: Scripts may still need to be read by Claude for patching or environment-specific adjustments
References (references/)
Documentation and reference material intended to be loaded as needed into context to inform Claude's process and thinking.
When to include: For documentation that Claude should reference while working
Examples: references/finance.md for financial schemas, references/mnda.md for company NDA template, references/policies.md for company policies, references/api_docs.md for API specifications
Use cases: Database schemas, API documentation, domain knowledge, company policies, detailed workflow guides
Benefits: Keeps SKILL.md lean, loaded only when Claude determines it's needed
Best practice: If files are large (>10k words), include grep search patterns in SKILL.md
Avoid duplication: Information should live in either SKILL.md or references files, not both. Prefer references files for detailed information unless it's truly core to the skill—this keeps SKILL.md lean while making information discoverable without hogging the context window. Keep only essential procedural instructions and workflow guidance in SKILL.md; move detailed reference material, schemas, and examples to references files.
Assets (assets/)
Files not intended to be loaded into context, but rather used within the output Claude produces.
When to include: When the skill needs files that will be used in the final output
Examples: assets/logo.png for brand assets, assets/slides.pptx for PowerPoint templates, assets/frontend-template/ for HTML/React boilerplate, assets/font.ttf for typography
Use cases: Templates, images, icons, boilerplate code, fonts, sample documents that get copied or modified
Benefits: Separates output resources from documentation, enables Claude to use files without loading them into context
Progressive Disclosure Design Principle
Skills use a three-level loading system to manage context efficiently:
Metadata (name + description) - Always in context (~100 words)
SKILL.md body - When skill triggers (<5k words)
Bundled resources - As needed by Claude (Unlimited*)
*Unlimited because scripts can be executed without reading into context window.
Claude Search Optimization (CSO)
Critical for discovery: Future Claude needs to FIND your skill
1. Rich Description Field
Purpose: Claude reads description to decide which skills to load for a given task. Make it answer: "Should I read this skill right now?"
Format: Start with "Use when..." to focus on triggering conditions, then explain what it does
Content:
Use concrete triggers, symptoms, and situations that signal this skill applies
Describe the problem (race conditions, inconsistent behavior) not language-specific symptoms (setTimeout, sleep)
Keep triggers technology-agnostic unless the skill itself is technology-specific
If skill is technology-specific, make that explicit in the trigger
Write in third person (injected into system prompt)
# ❌ BAD: Too abstract, vague, doesn't include when to usedescription:Forasynctesting# ❌ BAD: First persondescription:Icanhelpyouwithasynctestswhenthey'reflaky# ❌ BAD: Mentions technology but skill isn't specific to itdescription:UsewhentestsusesetTimeout/sleepandareflaky# ✅ GOOD: Starts with "Use when", describes problem, then what it doesdescription:Usewhentestshaveraceconditions,timingdependencies,orpass/failinconsistently-replacesarbitrarytimeoutswithconditionpollingforreliableasynctests# ✅ GOOD: Technology-specific skill with explicit triggerdescription:UsewhenusingReactRouterandhandlingauthenticationredirects-providespatternsforprotectedroutesandauthstatemanagement
✅ testing-skills-with-subagents not subagent-skill-testing
4. Token Efficiency (Critical)
Problem: getting-started and frequently-referenced skills load into EVERY conversation. Every token counts.
Target word counts:
getting-started workflows: <150 words each
Frequently-loaded skills: <200 words total
Other skills: <500 words (still be concise)
Techniques:
Move details to tool help:
# ❌ BAD: Document all flags in SKILL.md
search-conversations supports --text, --both, --after DATE, --before DATE, --limit N
# ✅ GOOD: Reference --help
search-conversations supports multiple modes and filters. Run --helpfor details.
Use cross-references:
# ❌ BAD: Repeat workflow details
When searching, dispatch subagent with template...
[20 lines of repeated instructions]
# ✅ GOOD: Reference other skill
Always use subagents (50-100x context savings). REQUIRED: Use [other-skill-name] for workflow.
Compress examples:
# ❌ BAD: Verbose example (42 words)
your human partner: "How did we handle authentication errors in React Router before?"
You: I'll search past conversations for React Router authentication patterns.
[Dispatch subagent with search query: "React Router authentication error handling 401"]
# ✅ GOOD: Minimal example (20 words)
Partner: "How did we handle auth errors in React Router?"
You: Searching...
[Dispatch subagent → synthesis]
Eliminate redundancy:
Don't repeat what's in cross-referenced skills
Don't explain what's obvious from command
Don't include multiple examples of same pattern
Verification:
wc -w skills/path/SKILL.md
# getting-started workflows: aim for <150 each# Other frequently-loaded: aim for <200 total
Why no @ links:@ syntax force-loads files immediately, consuming 200k+ context before you need them.
Flowchart Usage
digraph when_flowchart {
"Need to show information?" [shape=diamond];
"Decision where I might go wrong?" [shape=diamond];
"Use markdown" [shape=box];
"Small inline flowchart" [shape=box];
"Need to show information?" -> "Decision where I might go wrong?" [label="yes"];
"Decision where I might go wrong?" -> "Small inline flowchart" [label="yes"];
"Decision where I might go wrong?" -> "Use markdown" [label="no"];
}
Recognition scenarios: Do they recognize when pattern applies?
Application scenarios: Can they use the mental model?
Counter-examples: Do they know when NOT to apply?
Success criteria: Agent correctly identifies when/how to apply pattern
Reference Skills (documentation/APIs)
Examples: API documentation, command references, library guides
Test with:
Retrieval scenarios: Can they find the right information?
Application scenarios: Can they use what they found correctly?
Gap testing: Are common use cases covered?
Success criteria: Agent finds and correctly applies reference information
Bulletproofing Skills Against Rationalization
Skills that enforce discipline (like TDD) need to resist rationalization. Agents are smart and will find loopholes when under pressure.
Psychology note: Understanding WHY persuasion techniques work helps you apply them systematically. See persuasion-principles.md for research foundation (Cialdini, 2021; Meincke et al., 2025) on authority, commitment, scarcity, social proof, and unity principles.
Close Every Loophole Explicitly
Don't just state the rule - forbid specific workarounds:
No exceptions:
Don't keep it as "reference"
Don't "adapt" it while writing tests
Don't look at it
Delete means delete
</Good>
### Address "Spirit vs Letter" Arguments
Add foundational principle early:
```markdown
**Violating the letter of the rules is violating the spirit of the rules.**
This cuts off entire class of "I'm following the spirit" rationalizations.
Build Rationalization Table
Capture rationalizations from baseline testing (see Testing section below). Every excuse agents make goes in the table:
| Excuse | Reality |
|--------|---------|
| "Too simple to test" | Simple code breaks. Test takes 30 seconds. |
| "I'll test after" | Tests passing immediately prove nothing. |
| "Tests after achieve same goals" | Tests-after = "what does this do?" Tests-first = "what should this do?" |
Create Red Flags List
Make it easy for agents to self-check when rationalizing:
## Red Flags - STOP and Start Over- Code before test
- "I already manually tested it"
- "Tests after achieve the same purpose"
- "It's about spirit not ritual"
- "This is different because..."
**All of these mean: Delete code. Start over with TDD.**
Update CSO for Violation Symptoms
Add to description: symptoms of when you're ABOUT to violate the rule:
helper1, helper2, step3, pattern4
Why bad: Labels should have semantic meaning
STOP: Before Moving to Next Skill
After writing ANY skill, you MUST STOP and complete the deployment process.
Do NOT:
Create multiple skills in batch without testing each
Move to next skill before current one is verified
Skip testing because "batching is more efficient"
The deployment checklist below is MANDATORY for EACH skill.
Deploying untested skills = deploying untested code. It's a violation of quality standards.
Skill Creation Checklist (TDD Adapted)
IMPORTANT: Use TodoWrite to create todos for EACH checklist item below.
RED Phase - Write Failing Test:
Create pressure scenarios (3+ combined pressures for discipline skills)
Run scenarios WITHOUT skill - document baseline behavior verbatim
Identify patterns in rationalizations/failures
GREEN Phase - Write Minimal Skill:
Name uses only letters, numbers, hyphens (no parentheses/special chars)
YAML frontmatter with only name and description (max 1024 chars)
Description starts with "Use when..." and includes specific triggers/symptoms
Description written in third person
Keywords throughout for search (errors, symptoms, tools)
Clear overview with core principle
Address specific baseline failures identified in RED
Code inline OR link to separate file
One excellent example (not multi-language)
Run scenarios WITH skill - verify agents now comply
REFACTOR Phase - Close Loopholes:
Identify NEW rationalizations from testing
Add explicit counters (if discipline skill)
Build rationalization table from all test iterations
Create red flags list
Re-test until bulletproof
Quality Checks:
Small flowchart only if decision non-obvious
Quick reference table
Common mistakes section
No narrative storytelling
Supporting files only for tools or heavy reference
Deployment:
Commit skill to git and push to your fork (if configured)
Consider contributing back via PR (if broadly useful)
Discovery Workflow
How future Claude finds your skill:
Encounters problem ("tests are flaky")
Finds SKILL (description matches)
Scans overview (is this relevant?)
Reads patterns (quick reference table)
Loads example (only when implementing)
Optimize for this flow - put searchable terms early and often.
The Bottom Line
Creating skills IS TDD for process documentation.
Same Iron Law: No skill without failing test first.
Same cycle: RED (baseline) → GREEN (write skill) → REFACTOR (close loopholes).
Same benefits: Better quality, fewer surprises, bulletproof results.
If you follow TDD for code, follow it for skills. It's the same discipline applied to documentation.
Skill Creation Process
To create a skill, follow the "Skill Creation Process" in order, skipping steps only if there is a clear reason why they are not applicable.
Step 1: Understanding the Skill with Concrete Examples
Skip this step only when the skill's usage patterns are already clearly understood. It remains valuable even when working with an existing skill.
To create an effective skill, clearly understand concrete examples of how the skill will be used. This understanding can come from either direct user examples or generated examples that are validated with user feedback.
For example, when building an image-editor skill, relevant questions include:
"What functionality should the image-editor skill support? Editing, rotating, anything else?"
"Can you give some examples of how this skill would be used?"
"I can imagine users asking for things like 'Remove the red-eye from this image' or 'Rotate this image'. Are there other ways you imagine this skill being used?"
"What would a user say that should trigger this skill?"
To avoid overwhelming users, avoid asking too many questions in a single message. Start with the most important questions and follow up as needed for better effectiveness.
Conclude this step when there is a clear sense of the functionality the skill should support.
Step 2: Planning the Reusable Skill Contents
To turn concrete examples into an effective skill, analyze each example by:
Considering how to execute on the example from scratch
Identifying what scripts, references, and assets would be helpful when executing these workflows repeatedly
Example: When building a pdf-editor skill to handle queries like "Help me rotate this PDF," the analysis shows:
Rotating a PDF requires re-writing the same code each time
A scripts/rotate_pdf.py script would be helpful to store in the skill
Example: When designing a frontend-webapp-builder skill for queries like "Build me a todo app" or "Build me a dashboard to track my steps," the analysis shows:
Writing a frontend webapp requires the same boilerplate HTML/React each time
An assets/hello-world/ template containing the boilerplate HTML/React project files would be helpful to store in the skill
Example: When building a big-query skill to handle queries like "How many users have logged in today?" the analysis shows:
Querying BigQuery requires re-discovering the table schemas and relationships each time
A references/schema.md file documenting the table schemas would be helpful to store in the skill
To establish the skill's contents, analyze each concrete example to create a list of the reusable resources to include: scripts, references, and assets.
Step 3: Creating the Skill Directory
Skip this step if the skill already exists and only needs iteration.
Create the skill directory and required files:
Create the skill folder: mkdir -p skills/<skill-name>
Create SKILL.md with YAML frontmatter:
---
name: skill-name
description: Use when [triggering conditions] - [what the skill does]
---# Skill Name## Critical Guidlines
[Core principle in 1-2 sentences. Each start wit "You MUST ..."]
## How to Use
[Think in steps, use problem decomposition, etc.]
## Guide
[Procedures, patterns]
## Examples
[Examples of how to use the skill, include agent input and output]
## Troubleshooting
[Common mistakes and how to avoid them]
## Resources
[Scripts, references, assets]
Add resource subdirectories only if needed:
scripts/ — reusable executable code
references/ — documentation loaded on demand
assets/ — files used in output (templates, images)
Step 4: Edit the Skill
When editing the (newly-generated or existing) skill, remember that the skill is being created for another instance of Claude to use. Focus on including information that would be beneficial and non-obvious to Claude. Consider what procedural knowledge, domain-specific details, or reusable assets would help another Claude instance execute these tasks more effectively.
Start with Reusable Skill Contents
To begin implementation, start with the reusable resources identified above: scripts/, references/, and assets/ files. Note that this step may require user input. For example, when implementing a brand-guidelines skill, the user may need to provide brand assets or templates to store in assets/, or documentation to store in references/.
Remove any resource subdirectories not needed for the skill. Most skills need only SKILL.md.
Update SKILL.md
Writing Style: Write the entire skill using imperative/infinitive form (verb-first instructions), not second person. Use objective, instructional language (e.g., "To accomplish X, do Y" rather than "You should do X" or "If you need to do X"). This maintains consistency and clarity for AI consumption.
To complete SKILL.md, answer the following questions:
What is the purpose of the skill, in a few sentences?
When should the skill be used?
In practice, how should Claude use the skill? All reusable skill contents developed above should be referenced so that Claude knows how to use them.
Step 5: Validating the Skill
Before deploying, verify the skill meets requirements:
Frontmatter — YAML contains only name and description (max 1024 chars total)
Name — uses only letters, numbers, and hyphens
Description — starts with "Use when...", written in third person, includes specific triggers
Structure — SKILL.md exists at skills/<skill-name>/SKILL.md
Resources — any referenced scripts, references, or assets exist at their declared paths
Step 6: Iterate
After testing the skill, users may request improvements. Often this happens right after using the skill, with fresh context of how the skill performed.
Iteration workflow:
Use the skill on real tasks
Notice struggles or inefficiencies
Identify how SKILL.md or bundled resources should be updated
