What Are Claude Skills? A Complete Beginner's Guide

Last updated: December 2025

If you've been using Claude and wondered why it sometimes feels like starting from scratch with every conversation, you're not alone. That's exactly the problem Claude Skills solve.

In this guide, we'll break down everything you need to know about Skills: what they are, how they work, and why they're becoming the most powerful way to customize AI agents.

TL;DR

Claude Skills are reusable instruction packages that teach Claude specialized workflows and domain expertise. Think of them as "muscle memory" for AI - instead of explaining your preferences every time, Skills let Claude automatically apply your standards, processes, and knowledge when relevant.

The Problem Skills Solve

Here's a scenario every Claude user has experienced:

You spend 20 minutes explaining your coding standards to Claude
Claude writes perfect code following your guidelines
Next conversation: Claude has completely forgotten everything
Repeat forever

This isn't a bug - it's how LLMs work. They don't retain memory between conversations. Every session starts fresh.

Skills fix this permanently.

With Skills, Claude can:

Automatically apply your code style preferences
Follow your testing workflows without reminders
Use your templates for documents and presentations
Execute multi-step procedures reliably

What Exactly Is a Skill?

At its core, a Skill is just a folder containing a SKILL.md file. That's it.

my-skill/
├── SKILL.md          # Required: instructions + metadata
├── scripts/          # Optional: executable code
├── references/       # Optional: additional docs
└── assets/           # Optional: templates, examples

The SKILL.md file has two parts:

1. YAML Frontmatter (metadata Claude always sees):

---
name: code-reviewer
description: Reviews code for security vulnerabilities, performance issues, 
  and style violations. Use when reviewing pull requests or auditing code.
---

2. Markdown Instructions (loaded when the skill is triggered):

# Code Review Process

## Step 1: Security Scan
Check for common vulnerabilities:
- SQL injection
- XSS attacks
- Hardcoded secrets
...

The genius is in the progressive disclosure:

What Loads	When	Token Cost
Name + description	Always	~100 tokens
Full instructions	When triggered	~500-5000 tokens
Reference files	As needed	Unlimited

This means you can install dozens of Skills without burning through your context window. Claude only loads what's relevant for the current task.

Skills vs. Everything Else

If you're coming from other AI tools, here's how Skills compare:

Skills vs. GPT Custom Instructions

	Claude Skills	GPT Custom Instructions
Persistence	Across all conversations	Single conversation
Can include code	Yes	No
File bundling	Unlimited reference files	No
Context efficiency	Loads only when relevant	Always consumes context

Skills vs. CLAUDE.md Files

Both customize Claude, but for different purposes:

CLAUDE.md: Project-specific context that's always loaded (build commands, file structure, conventions)
Skills: Reusable workflows that load on-demand across any project

Think of CLAUDE.md as "what you need to know about this codebase" and Skills as "how to do specific tasks."

Skills vs. MCP (Model Context Protocol)

This is a common confusion:

MCP: Gives Claude access to external data and tools
Skills: Teaches Claude what to do with that data

They're complementary. MCP without Skills = powerful but generic. Skills without MCP = knowledgeable but limited.

Real Examples of Useful Skills

Development Skills

TDD Workflow - Forces test-driven development:

When implementing any feature:
1. Write failing tests FIRST
2. Implement minimum code to pass
3. Refactor only after tests pass
4. Never write implementation before tests exist

Systematic Debugging - Prevents random fix attempts:

When debugging:
1. Reproduce the issue reliably
2. Identify the root cause (not symptoms)
3. Write a test that captures the bug
4. Fix and verify the test passes

Document Skills

Anthropic provides official Skills for:

Excel/xlsx - Create spreadsheets with formulas and charts
PowerPoint/pptx - Generate presentations with branding
Word/docx - Create formatted documents
PDF - Extract, fill forms, merge documents

Productivity Skills

Linear Issue Logging - One user described their setup:

"Now I just say 'log that auth bug' and it creates the issue with correct labels, deeplinks to relevant docs, and assigns to the right team"

How to Install Skills

Claude.ai

Go to Settings > Features
Click "Add custom skill"
Upload your SKILL.md file or folder

Claude Code

# Clone a skill repo
git clone https://github.com/anthropics/skills ~/.claude/skills/official

# Or add to your project
mkdir -p .claude/skills
# Add your SKILL.md files there

Via Plugins

Skills can be packaged into plugins that bundle skills, slash commands, and MCP servers together. Check agentskills.io for the open standard specification.

Creating Your First Skill

The easiest way to create a Skill is to ask Claude:

"Help me create a skill for [your workflow]"

Claude will ask clarifying questions and generate the SKILL.md structure for you.

Manual Creation

Step 1: Define the trigger

What keywords or situations should activate this skill?

---
name: api-design
description: Designs RESTful APIs following company standards. Use when 
  creating new endpoints, designing API contracts, or reviewing API specs.
---

Step 2: Write clear instructions

Use markdown with headers, examples, and concrete steps:

# API Design Standards

## Naming Conventions
- Use plural nouns for resources: `/users`, `/orders`
- Use kebab-case: `/user-profiles` not `/userProfiles`

## Response Format
Always return:
```json
{
  "data": {},
  "meta": { "timestamp": "ISO-8601" }
}

Common Mistakes to Avoid

Don't use verbs in URLs
Don't nest resources more than 2 levels deep


**Step 3: Test and iterate**

The key insight from experienced users: start minimal and add detail based on what Claude gets wrong.

---

## Best Practices from Power Users

### 1. Keep Your Global CLAUDE.md Minimal

Put only universally-applicable rules in `~/.claude/CLAUDE.md`:

```markdown
- **Current date**: 2025-12-18
- **Git Commits**: Use conventional format
- **Style**: Prefer self-documenting code over comments

2. One Skill = One Job

Skills that try to do everything end up doing nothing well. Focus each skill on a single, specific workflow.

Good:

tdd-workflow - Just TDD practices
api-design - Just API conventions
code-review - Just review checklists

Bad:

everything-skill - TDD + API + review + deployment + ...

3. Write Descriptions Like Search Queries

Claude finds Skills by semantic matching. Include keywords users would actually say:

# Good
description: Creates unit tests for React components using Jest and 
  React Testing Library. Use when testing React, writing test cases, 
  or setting up component tests.

# Bad  
description: Helps with testing stuff.

4. Use Progressive Disclosure

Don't put everything in SKILL.md. Split into reference files:

testing-skill/
├── SKILL.md              # Core workflow (500 lines max)
├── references/
│   ├── jest-patterns.md  # Detailed Jest examples
│   ├── rtl-patterns.md   # React Testing Library patterns
│   └── mocking.md        # Mock strategies

Claude will read reference files only when needed.

The Skills Ecosystem

Official Skills

anthropics/skills - Anthropic's official library
Claude Skills Page - Pre-built document skills

Community Resources

awesome-claude-skills - Curated community skills
agentskills.io - Open standard specification

Skills as an Open Standard

Here's the exciting part: Anthropic released Agent Skills as an open standard. This means skills work across:

Claude.ai
Claude Code
Cursor
OpenCode
VS Code
And more

One skill, every platform. No vendor lock-in.

Common Pitfalls to Avoid

1. Skill Not Triggering

Symptoms: Claude ignores your skill even when relevant.

Fixes:

Check the description includes relevant keywords
Restart Claude Code (fixes 80% of issues)
Verify the skill is enabled in settings

2. CLAUDE.md Bloat

Symptoms: Slow responses, hitting token limits fast.

Fix: Move procedural knowledge to Skills (on-demand loading) and keep CLAUDE.md for essential project context only.

3. Vague Skills

Symptoms: Claude uses the skill but produces generic output.

Fix: Add concrete examples, specific constraints, and clear success criteria.

Security Considerations

Skills can include executable code. Before installing third-party skills:

Audit all files - Read through the SKILL.md and any scripts
Check for network calls - Watch for unexpected data exfiltration
Verify the source - Stick to trusted repositories
Sandbox first - Test in a non-critical environment

What's Next?

Skills represent a fundamental shift in how we work with AI. Instead of treating Claude as a blank slate every conversation, Skills let you build cumulative expertise that compounds over time.

The ecosystem is still young. The best skills haven't been written yet - maybe by you.

Ready to dive in?

Browse existing skills at agentskills.io
Install a few that match your workflow
Create your first custom skill for a task you repeat often
Share what you build with the community