Anthropic Builder Skills: Creating Extensions for Claude Code

Official skills: anthropics/skills

Anthropic provides a set of official skills designed to help developers extend Claude Code's capabilities. These builder and testing skills streamline common development workflows, from creating MCP servers to testing web applications. This guide covers four essential skills that every Claude Code user should know about.

MCP Builder

Repository: mcp-builder

The MCP Builder skill helps you create Model Context Protocol (MCP) servers. MCP servers extend Claude's capabilities by providing custom tools, resources, and prompts that Claude can use during conversations.

What It Does

Scaffolds new MCP server projects with proper structure
Generates TypeScript or Python server implementations
Creates tool definitions with proper schemas
Sets up configuration files for Claude Code integration

How to Use It

Invoke the skill when you want to create a new MCP server:

/mcp-builder

You can also provide context about what you're building:

/mcp-builder Create an MCP server for managing GitHub issues

The skill guides you through defining tools, their parameters, and their implementations. It produces a complete, working MCP server that you can install and use immediately with Claude Code.

Example Output

The skill generates projects with this structure:

my-mcp-server/
├── src/
│   └── index.ts
├── package.json
├── tsconfig.json
└── README.md

Skill Creator

Repository: skill-creator

The Skill Creator helps you build custom skills for Claude Code. Skills are reusable instruction sets that teach Claude how to handle specific tasks or workflows.

What It Does

Creates properly formatted skill markdown files
Defines skill metadata and trigger conditions
Structures instructions for optimal Claude comprehension
Sets up skill directories with correct naming conventions

How to Use It

Start the skill creator with:

/skill-creator

Or specify what kind of skill you want to build:

/skill-creator Create a skill for code review workflows

The skill walks you through defining:

Skill name and description - What the skill does
Trigger conditions - When Claude should use it
Instructions - Step-by-step guidance for Claude
Examples - Sample inputs and outputs

Skill Structure

Generated skills follow this format:

markdown---
name: my-skill
description: What this skill does
triggers:
  - pattern: "keyword or phrase"
---

# Instructions

Detailed instructions for Claude...

Web Artifacts Builder

Repository: web-artifacts-builder

The Web Artifacts Builder skill creates interactive web components and standalone HTML applications. It specializes in generating self-contained artifacts that work without external dependencies.

What It Does

Generates complete HTML/CSS/JavaScript applications
Creates interactive visualizations and tools
Builds self-contained components with inline styles
Produces artifacts that run directly in browsers

How to Use It

Invoke it when you need web artifacts:

/web-artifacts-builder

Or describe what you want to build:

/web-artifacts-builder Create an interactive color palette generator

Use Cases

The Web Artifacts Builder excels at creating:

Data visualizations - Charts, graphs, and interactive displays
Utility tools - Calculators, converters, and formatters
Interactive demos - Proof-of-concept interfaces
Standalone widgets - Self-contained UI components

Output Format

Generated artifacts are single HTML files with embedded CSS and JavaScript:

html<!DOCTYPE html>
<html>
<head>
  <style>/* Embedded styles */</style>
</head>
<body>
  <!-- Component markup -->
  <script>/* Embedded logic */</script>
</body>
</html>

WebApp Testing

Repository: webapp-testing

The WebApp Testing skill provides structured approaches for testing web applications. It helps you create comprehensive test suites and validate application behavior.

What It Does

Designs test strategies for web applications
Creates end-to-end test scenarios
Generates test cases for common user flows
Identifies edge cases and potential failure points

How to Use It

Start a testing session with:

/webapp-testing

Or specify what you want to test:

/webapp-testing Test the authentication flow in my React app

Testing Approach

The skill helps you build tests across multiple levels:

Unit tests - Individual component behavior
Integration tests - Component interactions
End-to-end tests - Complete user workflows
Accessibility tests - WCAG compliance checks

Example Workflow

When testing a login form, the skill helps you cover:

Valid credential submission
Invalid username/password handling
Empty field validation
Rate limiting behavior
Session management
Error message display

Installing Official Skills

To use these skills, add the Anthropic skills repository to your Claude Code configuration:

bashclaude mcp add-skill anthropics/skills

Or install individual skills:

bashclaude mcp add-skill anthropics/skills/mcp-builder
claude mcp add-skill anthropics/skills/skill-creator
claude mcp add-skill anthropics/skills/web-artifacts-builder
claude mcp add-skill anthropics/skills/webapp-testing

Summary

These four official skills cover essential development workflows:

| Skill | Purpose | Primary Use Case | |-------|---------|------------------| | mcp-builder | Create MCP servers | Extending Claude's tools | | skill-creator | Build custom skills | Teaching Claude new workflows | | web-artifacts-builder | Generate web components | Creating interactive artifacts | | webapp-testing | Test web applications | Validating app behavior |

Each skill provides structured guidance that helps you accomplish complex tasks efficiently. By combining these skills, you can build a complete development workflow—from creating new tools and skills to building and testing web applications.

For more information on Claude Code skills and customization, visit the official Anthropic skills repository.