What Are AI Skills? SKILL.md, .cursorrules & Rules Files Explained

The Problem AI Skills Solve

Every developer has experienced this: you open a new chat with your AI assistant and have to re-explain everything. "I'm using TypeScript with strict mode. I prefer functional patterns. Always add error handling. Never use any."

Then tomorrow, new chat, repeat the whole thing.

AI Skills solve this. They're files in your project that load automatically every time you use your AI tool. Your preferences, standards, and expertise are always there — without you having to type them.

AI Skills vs System Prompts vs CLAUDE.md

There are three related but distinct concepts:

How to Write Your First Skill

Creating a skill is as simple as writing a text file. Here's a 3-minute guide for Claude Code:

1. Create a .claude/skills/ directory in your project
2. Create a file named typescript-expert.md
3. Add YAML frontmatter and your instructions:

---
name: typescript-expert
description: Expert TypeScript developer with strict patterns
---

You are an expert TypeScript developer. Always:
- Use TypeScript strict mode (no 'any' types, proper generics)
- Prefer type inference over explicit annotations where clear
- Use discriminated unions for complex state
- Add JSDoc comments for public APIs
- Write exhaustive type checks with never for impossible states

When asked to write TypeScript:
- Start with interfaces/types before implementation
- Use const assertions for literal types
- Handle null/undefined explicitly — no non-null assertions (!)

That's it. Claude Code will now automatically apply these patterns whenever it writes TypeScript in your project.

What Makes a Good Skill?

• Specific, not generic — "Use React 18 Server Components for data fetching" beats "be a good developer"
• Action-oriented — Start with verbs: "Always..., Never..., Prefer..., When X, do Y"
• Single responsibility — One skill per topic. A "TypeScript Expert" skill, not a "TypeScript + React + Testing" skill
• Shareable — Write skills your whole team can use, not just personal preferences

Frequently Asked Questions

Do AI Skills work with all AI tools?

Each tool has its own format: SKILL.md for Claude Code, .cursorrules for Cursor, .windsurfrules for Windsurf, .github/copilot-instructions.md for VS Code Copilot. The concept is universal but the file format varies.

Can I share Skills with my team?

Yes — that's one of the best things about Skills. Commit them to your project repo and every team member automatically gets the same AI behavior. This standardizes code quality across your team.

Do Skills work together with MCP?

Yes — and they're complementary. MCP gives your AI access to tools (GitHub, databases, search). Skills tell it how to use those tools according to your team's standards. See our MCP + Skills workflow guide.