What Are Claude Skills? A Deep Dive into Anthropic’s New Engineering Paradigm for AI Agents

A relatively new project on Anthropic’s GitHub is gaining significant traction: https://github.com/anthropics/skills. The project revolves around a new concept called “Skills,” which I believe is fundamentally an engineered structure for implementing AI agents.

It provides a new engineering paradigm for completing sub-tasks, much like a good design pattern in C++ solves a common, recurring problem.

1. What Are “Skills”?

A “Skill” is a “skill pack” composed of instruction documents, scripts, and resources. Claude can dynamically load these Skills on demand to improve its consistency and performance on specific, repeatable tasks.

With Skills, Claude can reliably execute tasks in a reusable way, such as:

• Writing a document according to a company’s specific brand guidelines.
• Analyzing data following an organization’s internal processes.
• Automating a personal workflow.

How Skills Work

Skills operate on an “on-demand” basis. When you initiate a task, Claude reviews the available Skills, automatically selects the relevant ones, and loads only the instructions and resources needed to complete that specific task.

This “just-in-time” approach increases speed and effectiveness while avoiding the problem of stuffing the context window with irrelevant information, keeping the conversation and computation efficient and stable.

The Core Mechanism:

1. You make a task request.
2. Claude matches and selects from its available Skills.
3. It dynamically loads only the relevant instructions, scripts, and resources for the chosen Skill(s).
4. It executes the task following the Skill’s process, improving consistency and quality.

Key Advantages:

• Improved Task Performance: Provides specialized capabilities for document creation, data analysis, and domain-specific tasks, supplementing the general model’s knowledge.
• Institutional Knowledge Capture: Allows organizations to package their processes, best practices, and institutional knowledge, ensuring both team members and Claude adhere to the same standards.
• Easy to Customize: You can create basic Skills using Markdown. For advanced functionality, you can attach executable scripts.
• Composable: For complex tasks, Claude can automatically combine multiple Skills.

The SKILL.md Template File:

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

# My Skill Name

[Add your instructions here that Claude will follow when this skill is active]

## Examples
- Example usage 1
- Example usage 2

## Guidelines
- Guideline 1
- Guideline 2

2. How Skills Compare to Other Claude Features

This new framework fits into the existing Claude ecosystem, but it’s important to understand the distinctions.

• Skills vs. Projects:
  • Projects: Provide “continuously loaded” static background knowledge for a specific, ongoing conversation or project.
  • Skills: Provide “on-demand activation” of specialized processes and operating guidelines that can be dynamically used in any conversation.
• Skills vs. MCP (Model Context Protocol):
  • MCP: Connects Claude to external services and data sources (the “tools”).
  • Skills: Provide the “how-to” procedural knowledge and operational steps.
  • Synergy: They work together. MCP gives Claude a tool, and a Skill teaches Claude how to use that tool effectively.
• Skills vs. Prompts:
  • Prompts (Custom Instructions): Apply to all conversations and emphasize general preferences and style.
  • Skills: Are task-specific and loaded only when relevant, making them much better for professional workflows and specialized processes.

3. The Skills Directory Structure

A Skill is defined by a simple directory structure:

my-skill/
├── SKILL.md (required)
├── reference.md (optional documentation)
├── examples.md (optional examples)
├── scripts/
│   └── helper.py (optional utility)
└── templates/
    └── template.txt (optional template)

3.1 Basic Structure Every Skill must have a directory and a SKILL.md file inside it.

3.2 Metadata (YAML Frontmatter) The SKILL.md file must begin with YAML frontmatter containing at least two required fields:

• name (Required): A human-readable name (≤ 64 chars). Ex: Brand Guidelines
• description (Required): A clear description of the Skill’s purpose and, crucially, when to use it (≤ 200 chars). Claude uses this description to decide when to activate the Skill. Ex: Apply Acme Corp brand guidelines to presentations and documents, including official colors, fonts, and logo usage.
• version (Optional): Version number (e.g., 1.0.0) for tracking changes.
• dependencies (Optional): Required software packages. Ex: python>=3.8, pandas>=1.5.0

3.3 The SKILL.md Body This is where the Skill’s instructions live. Claude only loads this body text if the description (metadata) alone isn’t enough to perform the task. This is key to saving context.

The body can include:

• Step-by-step execution procedures.
• Detailed rules and guidelines.
• Examples of use.
• When not to use the Skill.
• References to other resource files.

SKILL.md sample:

## Metadata
name: Brand Guidelines
description: Apply Acme Corp brand guidelines to all presentations and documents
version: 1.0.0

## Overview
This Skill provides Acme Corp's official brand guidelines for creating consistent, professional materials. When creating presentations, documents, or marketing materials, apply these standards to ensure all outputs match Acme's visual identity. Claude should reference these guidelines whenever creating external-facing materials or documents that represent Acme Corp.

## Brand Colors

Our official brand colors are:
- Primary: #FF6B35 (Coral)
- Secondary: #004E89 (Navy Blue)
- Accent: #F7B801 (Gold)
- Neutral: #2E2E2E (Charcoal)

## Typography

Headers: Montserrat Bold
Body text: Open Sans Regular
Size guidelines:
- H1: 32pt
- H2: 24pt
- Body: 11pt

## Logo Usage

Always use the full-color logo on light backgrounds. Use the white logo on dark backgrounds. Maintain minimum spacing of 0.5 inches around the logo.

## When to Apply

Apply these guidelines whenever creating:
- PowerPoint presentations
- Word documents for external sharing
- Marketing materials
- Reports for clients

## Resources

See the resources folder for logo files and font downloads.

3.4 Skill Resources

• Documentation: For complex information, you can split supplementary materials into separate files (REFERENCE.md, CHECKLIST.md, TEMPLATES/). Claude will load these on-demand if the SKILL.md references them.
• Executable Scripts: Advanced Skills can include executable code (e.g., in scripts/) that Claude can call to perform complex tasks like data cleaning, visualization, or batch processing using Python (pandas, numpy) or JavaScript (Node.js).

4. How to Use Skills in Claude

Before Uploading:

1. Read through your SKILL.md to ensure instructions are clear and complete.
2. Confirm the description accurately describes when the Skill should be used.
3. Check all file paths and references.
4. Test locally by giving Claude prompts that should trigger the Skill.

After Uploading:

1. Enable the Skill in Settings > Capabilities.
2. Validate it with various prompts that should trigger it.
3. Confirm Claude’s response indicates the Skill was loaded (e.g., it follows the Skill’s process).
4. If it doesn’t trigger as expected, iterate on the description and instructions to be more specific.

5. Best Practices for a Good “Skill”

• Be Clear: Instructions must be clear and consistently executable by Claude.
• Be Focused: Target one well-defined, repeatable task. Create small, focused Skills (one for each workflow) as they are easier to combine and reuse.
• Be Specific: The description is critical. Clearly state the “who, what, when” and any exceptions to help Claude make the right decision.
• Start Simple: Get the skeleton working with Markdown instructions first, then gradually add scripts and complex logic.
• Add Examples: Include typical inputs/outputs in SKILL.md to help align Claude on what “success” looks like.
• Use Versioning: Maintain the version field.
• Test Incrementally: Validate after every significant change.

6. Official Example: webapp-testing

The official GitHub repo has over 20 examples. A powerful one is webapp-testing, which uses Playwright to test web applications.

Its SKILL.md description clearly states its purpose:

---
name: webapp-testing
description: Toolkit for interacting with and testing local web applications using Playwright. Supports verifying frontend functionality, debugging UI behavior, capturing browser screenshots, and viewing browser logs.
...
---

A key part of its SKILL.md body is a Decision Tree that tells Claude exactly how to approach the task:

## Decision Tree: Choosing Your Approach

User task → Is it static HTML?
    ├─ Yes → Read HTML file directly to identify selectors
    │       ├─ Success → Write Playwright script using selectors
    │       └─ Fails/Incomplete → Treat as dynamic (below)
    │
    └─ No (dynamic webapp) → Is the server already running?
        ├─ No → Run: python scripts/with_server.py --help
        │        Then use the helper + write simplified PlayDwright script
        │
        └─ Yes → Reconnaissance-then-action:
            1. Navigate and `waitfor networkidle`
            2. Take screenshot or inspect DOM
            3. Identify selectors from rendered state
            4. Execute actions with discovered selectors

This structured logic is exactly what makes Skills superior to a simple prompt.

7. Conclusion

Claude Skills provide a true engineering paradigm.

In the past, developers have tried to chain functions using various MCPs, Agents, and prompt-glue. This approach is often unstable and difficult to maintain or inherit.

The Skills framework solves this by enforcing an engineering-first standard, which goes a long way toward solving the problem of “AI project engineering.”

Each Skill directory is like a small, self-contained Agent. These Skills can then be combined by Claude to create a complex Agent. It’s the same way we write software: we build foundational libraries (Skills) and then compose them to build complex applications. This is the natural and necessary evolution from a world of chaotic prompting to one of standardized, reliable AI engineering.

Reference sources:

• https://docs.claude.com/en/docs/claude-code/skills
• https://github.com/anthropics/skills