Skill (Claude Skills)

A Claude Skill is a folder containing a SKILL.md file (and optional supporting files) that defines a named capability Claude can invoke. The SKILL.md has YAML frontmatter with metadata — name, description, when to use it — and a markdown body with instructions, examples, and links to helpers. Drop it in ~/.claude/skills/ and Claude can use it. Skills are essentially structured, installable prompts. When a user's request matches a skill's description, Claude loads the skill body into context and follows its instructions. Think of them as the "apps" of the Claude ecosystem — discrete, shareable units of capability that don't require API keys, fine-tuning, or running a server. The format was introduced as part of Claude's broader push toward customizability without complexity. Compared to MCP servers (which expose tools and require running code), skills are pure markdown — easier to author, share, and version-control. Compared to custom GPTs (OpenAI's equivalent on the assistant side), skills are file-based and work in Claude Code, Claude Desktop, and the API equally. In practice teams use skills for: codifying internal style guides ("write a PR description like our team does"), wrapping common workflows ("triage a bug report"), and embedding domain knowledge ("explain this FERC regulation"). They're a low-friction way to make an LLM consistently good at something specific.