Skills in Claude Code: Extend Capability Without Writing Agents

What a Skill Is

A skill is a bundled set of instructions and tool definitions that extends Claude Code's behavior in a specific domain. Rather than writing a detailed prompt every time you want Claude Code to do something structured — like a code review or test generation — you enable a skill that knows how to do that thing well.

Built-in Skills

Claude Code ships with a set of built-in skills available without additional installation. Enable one with:

claude --skill testing
claude --skill architecture-review
claude --skill refactor

The testing skill, for example, includes instructions for writing comprehensive tests, specific guidance on common test patterns for different languages, and awareness of your test framework and assertion library.

Creating Custom Skills

Create a skill by making a directory with a skill.md file:

skills/
  my-custom-skill/
    skill.md  # Contains instructions and tool definitions
    prompts/
      task1.md
      task2.md

Reference it with --skill-path ./skills/my-custom-skill.

Skill vs Agent

Skills are lighter than agents — they do not run their own loop. They provide structured guidance to the main Claude Code session. For most tasks, a skill is what you want. Agents are for fully autonomous operations where you want the AI to drive without stopping for input.