Harvested from Claude Code's skill-authoring spec: - when_to_use frontmatter field (trigger phrases) on all 3 SKILL.md templates + github catalog exemplar; discovery scan surfaces it so agents see triggers without loading the full body. - Per-step 'Done when:' success criteria in the Steps section. - 'Use when / Do NOT use when' structure in the When to Use section. 252/252 tests pass.