What Are Skills?

A skill transforms Claude from a capable generalist into a specialist here is exactly how it works

When you ask Claude Code to "build a beautiful website," Claude draws on its general training. It knows HTML and CSS. It has seen thousands of websites. It will build something reasonable.

But reasonable is not the same as professional.

A skill changes this. A skill is a markdown file that contains expert-level instructions for a specific task. When that skill is active, Claude reads it before executing any work in that area. It stops being a generalist and starts operating as a specialist.

The Simple Explanation

Think of a skill as a briefing document for a specific type of expert.

The frontend design skill written by Anthropic's own design team contains everything a senior web designer would know: the patterns to avoid, the principles to follow, and the exact checks to run before finishing. When you activate it Claude builds websites the way that designer would, not the way a generic AI would.

The copywriting skill contains principles from 100 years of direct response marketing covering headline formulas, persuasion frameworks, and what makes people click. When you activate it the copy Claude writes is structurally sound and not just fluent.

You are not changing what Claude knows. You are focusing what it applies.

What Skills Look Like

A skill is just a plain text file with a .md extension. Here is a simplified example of what the inside of a skill looks like:

# Frontend Design Expert

You are a senior frontend designer with 15 years of experience. When building

any UI component or page, you apply these principles without being asked:

## Always Do

• Use a type scale with clear hierarchy (never arbitrary font sizes)
• Build mobile-first, then enhance for desktop
• Limit to 2 font families maximum
• Every interactive element must have a visible hover and focus state

## Never Do

• Use purple or blue gradient backgrounds (vibe-coded pattern)
• Glassmorphism effects
• Neon text glow
• Place important actions below the fold

## After Every Build

• Does the mobile view look intentional, not shrunken?
• Is the color palette consistent across all sections?
• Are all fonts loading from Google Fonts?

That is it. A list of expert rules formatted in markdown. When Claude reads it, it treats those rules as standing instructions for every piece of work that falls in that domain.

Two Types of Skills

Official skills are built by Anthropic or trusted sources. They are available directly in the Claude Code Desktop App, tested, reliable, and ready to use. The frontend design skill is the most popular example.

Custom skills are markdown files you write yourself. They are stored in a folder Claude Code watches. You define what they do, when to use them, and what rules they enforce. Building your own is covered later in this course.

How Skills Are Different From CLAUDE.md

You already know about CLAUDE.md which is the memory file Claude reads at the start of every session.

The differences are:

CLAUDE.md is scoped to the current project. A skill works across any project. CLAUDE.md contains your project context, preferences, and rules. A skill contains expert instructions for a specific task type. CLAUDE.md is always activated automatically. A skill is activated when you reference it in your prompt. CLAUDE.md is written by you. A skill can be written by you, Anthropic, or the community.

CLAUDE.md tells Claude about your project. Skills tell Claude how to do a specific type of work at a professional level. Both work together: your CLAUDE.md defines the project and the skill defines the quality of execution.

Your Action Right Now

Think about the last piece of work where Claude gave you a result that was technically correct but felt generic.

A skill would have prevented that. Hold that example in mind because you will use it to test your first skill in the next lesson.