SKILL.md must be included in every Skill bundle. Publishing is rejected if it's empty.

Don't put YAML front matter inside SKILL.md itself — metadata like name and version belongs separately in metadata.yaml. A file encoded with a BOM is also rejected.

Hermes loads the entire SKILL.md, so there's a character limit. For a long description that exceeds the limit, it's better to split it out into a references/ folder rather than cramming everything into SKILL.md.