Use when creating a new skill, editing an existing skill, or reviewing a skill before it ships. Covers the Agent Skills file format (SKILL.md frontmatter, folder layout, progressive disclosure), how to write a description that triggers reliably, when to bundle scripts, and the effective-instruction patterns (gotchas, checklists, defaults-not-menus, validation loops). Use even when the request says 'turn this runbook into a skill', 'standardize this process', 'write a SKILL.md', or 'make this reusable', without naming the format.
