Modern AI Engineering

Lesson 11.9 · 23 min · video lesson

Agent Skills: Reusable Capabilities in Agentic Systems

How can one agent know how to fill PDF forms, follow your brand guide and run your release checklist, without stuffing all of that into every prompt?

In short: An Agent Skill is a folder with a SKILL.md file (a short name and description, then instructions) plus any scripts or reference files the task needs. The agent sees only each skill's name and description at first, and opens the full instructions and files only when a task needs them. This "progressive disclosure" lets one agent carry many skills while keeping its context window small.

What you will learn

  • The problem before Agent Skills
  • What are Agent Skills?
  • What is inside a Skill?
  • The description is the trigger
  • Progressive disclosure, the main idea
  • A Skill can carry real code
  • Where Skills live
  • How do we create our own Skill?
  • Agent Skills vs MCP
  • A real example
  • Importance of Agent Skills
  • Things we must be careful about
  • Summary

In this lesson

  1. The problem before Agent Skills
  2. What are Agent Skills, and what is inside one?
  3. The description is the trigger
  4. Progressive disclosure, the main idea
  5. A Skill can carry real code
  6. Where Skills live and how to create one
  7. Agent Skills vs MCP
  8. A real example and why Skills matter
  9. Things we must be careful about
  10. Common mistakes and how to spot them
  11. Practice: try it yourself
  12. Summary

Key terms in this lesson

Agent Skill
A folder of instructions, scripts and resources that an agent discovers and loads on demand for one kind of task.
SKILL.md
The required file of a skill: YAML frontmatter with name and description, then Markdown instructions.
Frontmatter
A block of key: value metadata between two --- lines at the top of a Markdown file.
Progressive disclosure
Loading information in layers: a short summary first, details only when the task needs them.
Context window
The maximum amount of text, in tokens, a model can read in one call.
MCP (Model Context Protocol)
An open protocol for connecting agents to external tools and data through servers.

This lesson is part of the Generative AI Engineering and Complete AI Engineer tracks. See plans and pricing to open the full lesson, its video, labs and quiz, or try the free lesson first (free account needed).

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