What Are Claude Skills?
Claude Skills are portable, reusable instruction files — written in Markdown as SKILL.md — that teach Claude how to perform specific tasks with expertise. Think of them as specialized knowledge packs that transform Claude from a general-purpose AI assistant into a domain expert.
How Skills Work
Every Claude Skill is defined by a single SKILL.md file that contains YAML frontmatter (metadata like the skill name, description, and trigger conditions) followed by detailed instructions in Markdown. When you install a skill, Claude reads these instructions and applies them whenever a matching task comes up.
For example, the official PDF Processing skill teaches Claude best practices for extracting text, merging documents, filling forms, and handling scanned PDFs. Instead of generic advice, Claude follows battle-tested procedures that produce reliable results every time.
Anatomy of a SKILL.md File
--- name: My Custom Skill description: What this skill does triggers: - keyword1 - keyword2 --- # Instructions Detailed instructions for Claude to follow when this skill is activated...
Where Can You Use Skills?
Skills work across the entire Claude ecosystem. In Claude Desktop and claude.ai, you upload skills as ZIP files through the Customize panel. In Claude Code (the CLI tool for developers), skills live as files in your ~/.claude/skills/ directory and are automatically detected. In Cowork, Claude's desktop automation mode, skills load from a shared skills folder.
Anthropic vs. Community Skills
Anthropic skills are created and maintained by Anthropic. They cover core document workflows (Word, Excel, PDF, PowerPoint), creative tools (algorithmic art, brand guidelines), and developer utilities (MCP server builder, web testing). These are rigorously tested and kept up to date.
Community skills are built by developers and power users worldwide. They range from niche tools like Terraform best practices and Stripe integration guides to creative workflows like nonfiction book factories and D3.js visualization helpers. Because the SKILL.md format is open and simple, anyone can create and share skills.
Why Skills Matter
Without skills, you'd need to repeat complex instructions every conversation. Skills encode your expertise once and apply it forever. They're also composable — you can install multiple skills and Claude will pick the right one based on context. A developer might have a Terraform skill, a CI/CD skill, and a security audit skill all active simultaneously.