Agent Skills Tutorial: Build AI Agent Capabilities Fast

Agent Skills tutorial - AI agent capabilities with modular building blocks

Agent Skills - Build reusable AI agent capabilities

Anthropic launched Agent Skills on December 18, 2025—an open standard that lets developers build reusable capabilities for AI agents using simple Markdown files. In just seven weeks, 25+ platforms including Microsoft (VS Code, GitHub), OpenAI (Codex, ChatGPT), Cursor, and Goose adopted the standard. The brilliance is in the simplicity: a folder with a SKILL.md file containing instructions and metadata. That’s it. No complex tooling, no vendor lock-in, just files that work across the entire AI agent ecosystem.

Before Agent Skills, developers rebuilt the same capabilities for every platform—Cursor, Claude Code, GitHub Copilot, repeat. Now it’s build once, deploy everywhere. This is trending on Hacker News today (#9, 407 points), and it’s not hype—it’s momentum.

What Are Agent Skills?

Agent Skills use “progressive disclosure” to keep agents fast while providing deep expertise. Think three-phase loading: At startup, agents load only skill metadata—just the name and description, roughly 100 tokens per skill. When a task matches, the agent loads the full SKILL.md instructions (recommended under 5000 tokens). Finally, referenced files or scripts load only when needed.

This approach means agents can have hundreds of available skills without performance degradation. However, without progressive disclosure, agents would choke on context bloat. With it, skills scale efficiently.

Moreover, the format itself is beautifully simple. According to the official specification, every skill requires just a folder structure:

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

Every skill starts with SKILL.md containing YAML frontmatter (name + description) and Markdown instructions. Furthermore, optional directories add scripts, documentation, or assets as complexity demands. Start simple, add layers as needed.

Building Your First Agent Skill

Creating a minimal Agent Skill takes under 20 lines. Here’s the simplest possible format from the Anthropic skills repository:

---
name: my-skill-name
description: A clear description of what this skill does and when to use it                                                                                                                                            
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