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Mastering Claude Code: How to Create and Add Custom Agent Skills

Skilllm Team6 min read
Minimalist dark mode illustration with subtle abstract geometric shapes representing custom agent skills for Claude Code

The release of Claude Code has changed the game for terminal-based AI. It’s not just a chatbot; it’s an agent with a filesystem and a shell. However, to get the most out of Claude, you need to provide it with "Discipline"—structured workflows that prevent the AI from rushing and ensure it follows your specific architectural patterns.

This is achieved through Claude Agent Skills. In this tutorial, we’ll show you how to build and integrate custom skills into your Claude Code environment.

What is a Claude Code Skill?

While a tool like an MCP Server gives Claude "hands" (the ability to connect to external data), a Skill gives Claude "wisdom."

A Claude Skill is a folder-based set of instructions that the agent discovers and loads dynamically. Claude uses a Progressive Disclosure pattern: it only scans the metadata of your skills initially. It only pulls the full, token-heavy instructions into its context window when it realizes your current task requires that specific skill.

The Skill Folder Hierarchy

Claude Code searches for skills in specific locations. To create a skill, you must follow this directory structure:

TEXT
my-claude-skill/
├── SKILL.md          (The core logic and triggers)
├── scripts/          (Executable Python or Bash tools)
├── references/       (Docs, schemas, or design patterns)
└── assets/           (Boilerplates or static files)

The SKILL.md Blueprint

Your SKILL.md must start with a YAML frontmatter. This is the most critical part, as it acts as the "trigger" for Claude to activate the skill.

SKILL.md
---
name: security-audit-pro
description: A specialized skill for performing deep security audits on Node.js/Express applications. Use this when the user asks to "check for vulnerabilities" or "review security."
---

# Security Audit Protocol
1. Search for any usage of `eval()` or `child_process.exec()`.
2. Check `package.json` for known outdated dependencies.
3. Verify that all API routes have a rate-limiting middleware.
4. Reference the internal standards in [references/security-checklist.md](./references/security-checklist.md).

How to Add Skills to Claude Code

Step 1: Choose Your Directory

Claude Code looks for skills in two primary places:

  • Global (All Projects): ~/.claude/skills/
  • Local (This Project Only): ./.claude/skills/

If these folders don't exist, create them:

BASH
mkdir -p .claude/skills/my-new-skill

Step 2: Initialize with the Skill Creator

A pro-tip for Claude Code users: you don't have to write the markdown yourself. You can use the built-in Skill Creator.

Simply start a Claude Code session and type:

"Help me create a new skill for [Your Task Name] that lives in ./.claude/skills/"

Claude will then interview you about the requirements, generate the SKILL.md, and even draft the necessary helper scripts in the /scripts folder.

Step 3: Verification

Once your files are in place, restart your Claude Code session. You can verify the skill is detected by typing the / command in the chat to see the list of available skills, or simply ask:

"What skills do you currently have access to?"

Why Use Skills Instead of CLAUDE.md?

You might be familiar with CLAUDE.md (the file used for project-wide rules). Here is why you should migrate complex workflows to Skills:

  1. Token Efficiency: CLAUDE.md is loaded into every message. Skills are only loaded when needed.
  2. Portability: You can package a skill and share it across different teams or projects by simply copying the folder.
  3. Executable Logic: Skills can contain their own dedicated Python scripts that Claude can run to perform deterministic tasks (like parsing a specific file format) without having to "hallucinate" the logic.

Find the Best Skills for Your Agent

Building a comprehensive "Skill Library" is the secret to a 10x developer workflow. If you want to skip the setup and get straight to a high-performing agent, browse our marketplace.

At Skilllm, we provide specialized Agent Skills designed specifically for Claude Code, including:

  • PR Reviewers that follow strict linting rules.
  • Test Generators that automatically write Jest or Pytest suites.
  • Refactoring Assistants that apply SOLID principles to legacy code.

Conclusion

Claude Code is a powerful engine, but custom Agent Skills are the fuel that makes it precise. By moving your "procedural knowledge" into SKILL.md files, you ensure that Claude handles your code with the same discipline and standards that you do.

Ready to upgrade your AI agent? Explore the latest community-tested capabilities at Skilllm.com and transform your CLI into a specialized engineering powerhouse.