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Module
Module 2 of 5Lesson 3 of 3~15 min

Anatomy of a SKILL.md

To write or judge a skill, you need to read the file it is made of and understand the role of each part. This lesson teaches you to decode the structure of a SKILL.md, understand what its main settings control and know what will still work if you switch tools.

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Lesson objective

By the end of this lesson, you will be able to identify the parts of a skill (frontmatter, body, reference files), explain what the main frontmatter fields do, including allowed-tools, and say what stays portable from one tool to another.

Topics covered

  • SKILL.md
  • frontmatter
  • allowed-tools
  • skill structure
  • skill portability

Where it fits

Understand skills and when to use them

What is a skill, how is it loaded, and when is it the right tool?

Lessons in this module

  1. What a skill is, and how Claude loads it
  2. Skill, CLAUDE.md, subagent, MCP or hook?
  3. Anatomy of a SKILL.md (this lesson)

What you will learn in the course

This lesson is part of the course Build reliable Claude Skills for your product work

  • Identify a recurring task that justifies a skill rather than a one-off prompt, and explain how the skill is loaded (progressive disclosure).
  • Choose and justify the right mechanism for a given need (skill, CLAUDE.md, subagent, MCP server, hook).
  • Write a name and description that trigger the skill at the right moment, and choose who can invoke it.
  • Design a complete SKILL.md (frontmatter, checkable rules, procedure, output format, reference files) from a scoping brief.
  • Configure a skill's pre-approved and removed tools according to risk, without confusing pre-approval with restriction.
  • Test a skill's triggering and output with evaluation scenarios, iterate, then measure its value over time.
  • Choose, audit and share skills (third-party or internal) while managing the security risks.

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