1.3What Agent Skills Are

Agent skills are reusable capability packages for AI coding agents: markdown files that teach the agent how to accomplish domain-specific tasks using tools it already has.

> KEY CONCEPT: Skills do not add new tools. They teach the agent how to use existing tools (primarily Bash, Read, and Write) for a specific domain. A browser automation skill teaches CLI commands for browser control. The tools are the same -- the knowledge is new.

One more property makes skills strategically important: portability. As of 2026, the SKILL.md format is a de facto cross-agent standard -- the same file works in Claude Code, Cursor, Gemini CLI, and Codex CLI. A skill written once travels with your team regardless of agent. That is why tool vendors now ship skills alongside their CLIs: playwright-cli install --skills generates a SKILL.md that teaches any skill-aware agent the entire browser command surface.