AgentSkills.site

SKM-F01 · Error

No YAML frontmatter block found

The file must open with a line containing only `---`, followed by YAML, followed by a closing `---`.

Check this in the validator →

What the rule is

A SKILL.md is a markdown file with YAML frontmatter, and the frontmatter is what tells an agent when the skill is relevant. Without a `---`-delimited block at the very top of the file, there's no frontmatter to read at all — not empty frontmatter, none.

This is different from a frontmatter block that's present but broken (SKM-F02–SKM-F04). Here, the opening delimiter line itself — a line containing only `---` — was never found, which usually means the file starts directly with prose, or the delimiter has stray characters on the same line.

Where it comes from

Which runtimes enforce it

RuntimeEffectNote
Claude CodeBreaks the skillWithout frontmatter there is no name or description — the two fields the format requires and the only ones a runtime sees at discovery time.
CodexBreaks the skillWithout frontmatter there is no name or description — the two fields the format requires and the only ones a runtime sees at discovery time.
CursorBreaks the skillWithout frontmatter there is no name or description — the two fields the format requires and the only ones a runtime sees at discovery time.
OpenClawBreaks the skillWithout frontmatter there is no name or description — the two fields the format requires and the only ones a runtime sees at discovery time.
Hermes AgentBreaks the skillWithout frontmatter there is no name or description — the two fields the format requires and the only ones a runtime sees at discovery time.

How to fix it

  • Add a line containing only `---` as the very first line of the file, followed by `name:` and `description:` fields, followed by a closing `---` line, before any body text.

Before

# My Skill

This does a thing.

After

---
name: my-skill
description: Use when asked to do the thing.
---

# My Skill

Instructions.

Elsewhere