SKM-K03 · Error
`compatibility` is longer than 500 characters
The specification caps `compatibility` at 500 characters.
What the rule is
The specification caps the optional `compatibility` field — used to state environment requirements like the intended product, system packages, or network access — at 500 characters.
No runtime documents what happens when this limit is exceeded; the constraint comes from the specification's own field table, and this rule flags the violation itself rather than a documented runtime consequence.
Where it comes from
- Agent Skills — SpecificationSpecification / reference validator
- skills-ref validate (official reference validator, v0.1.5)Specification / reference validator
Strict spec conformance
Non-conformant. The official reference validator (skills-ref) rejects this — tested directly, not inferred from severity.
This is a separate question from the severity above and from which runtimes enforce it below — a rule can be a real, working extension in its home runtime while the reference validator still rejects the file outright, or vice versa. Both facts are reported, never one inferred from the other.
Which runtimes enforce it
| Runtime | Effect | Note |
|---|---|---|
| Claude Code | Not documented | The spec states the limit and skills-ref hard-fails on it; no runtime documents what happens past it at load time. |
| Codex | Not documented | The spec states the limit and skills-ref hard-fails on it; no runtime documents what happens past it at load time. |
| Cursor | Not documented | The spec states the limit and skills-ref hard-fails on it; no runtime documents what happens past it at load time. |
| OpenClaw | Not documented | The spec states the limit and skills-ref hard-fails on it; no runtime documents what happens past it at load time. |
| Hermes Agent | Not documented | The spec states the limit and skills-ref hard-fails on it; no runtime documents what happens past it at load time. |
How to fix it
- Shorten `compatibility` to under 500 characters, keeping only the environment requirements that actually gate whether the skill can run.
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.