Agent Skills Specification: Universal SKILL.md Standard Works Across Claude Code, Cursor, Gemini CLI, Codex CLI — Install via npx skills add

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The Agent Skills open standard defines SKILL.md files with YAML frontmatter (trigger conditions) and markdown instructions that work across Claude Code, Cursor, Gemini CLI, Codex CLI, and Antigravity IDE. Claude Code extends the standard with invocation control, subagent execution, and dynamic context injection. Install any skill via `npx skills add <org>/<repo>` — the ecosystem now includes official, verified, and thousands of community-contributed skills.