SKM-F02 · Error
Frontmatter block is not closed
An opening `---` was found with no matching closing `---` line after it.
What the rule is
An opening `---` delimiter was found, but no second `---` line appears anywhere after it. Every implementation of the format needs both delimiters to know where the YAML ends and the markdown body begins — without the closing line, the parser has no way to tell.
This usually happens when a description field's multi-line value is indented incorrectly and swallows the closing delimiter, or when the closing `---` was accidentally deleted during an edit.
Where it comes from
- Agent Skills — SpecificationSpecification
Which runtimes enforce it
| Runtime | Effect | Note |
|---|---|---|
| Claude Code | Breaks the skill | An unterminated block can't be parsed as YAML by any implementation of the format. |
| Codex | Breaks the skill | An unterminated block can't be parsed as YAML by any implementation of the format. |
| Cursor | Breaks the skill | An unterminated block can't be parsed as YAML by any implementation of the format. |
| OpenClaw | Breaks the skill | An unterminated block can't be parsed as YAML by any implementation of the format. |
| Hermes Agent | Breaks the skill | An unterminated block can't be parsed as YAML by any implementation of the format. |
How to fix it
- Add a line containing only `---` immediately after the last frontmatter field and before the markdown body.
Elsewhere
- SKILL.md, the formatThe full frontmatter field table this rule is drawn from.
- Agent Skills Not WorkingThe diagnostic reference this rule’s portability and failure evidence comes from.
- All rulesEvery check the validator runs, grouped by class.