crewAIInc/crewAI · error · ValueError

No YAML frontmatter block found

Error message

No YAML frontmatter block found

What it means

The fallback frontmatter parser (used when the SDK's `crewai.skills.parser` is not importable) looks for a `^---\n...\n---` block at the very start of the file. If the regex does not match — no delimiters, a leading blank line/BOM, CRLF line endings, or `---` not on line 1 — it raises `ValueError("No YAML frontmatter block found")`, which surfaces as error 70's message.

Source

Thrown at lib/cli/src/crewai_cli/skills/main.py:398

        """Extract YAML frontmatter fields from a SKILL.md string.

        Reuses crewai.skills.parser when available, with a minimal
        fallback for environments where the full SDK isn't installed.
        """
        try:
            from crewai.skills.parser import parse_frontmatter

            fm_dict, _ = parse_frontmatter(content)
            return fm_dict
        except ImportError:
            pass

        # Fallback: minimal YAML parsing without SDK dependency
        import re

        match = re.match(r"^---\n(.*?)\n---", content, re.DOTALL)
        if not match:
            raise ValueError("No YAML frontmatter block found")
        try:
            import yaml

            return yaml.safe_load(match.group(1)) or {}
        except ImportError:
            result: dict[str, str] = {}
            for line in match.group(1).splitlines():
                if ":" in line:
                    key, _, value = line.partition(":")
                    result[key.strip()] = value.strip()
            return result

    def _read_version(self, skill_md: Path) -> str | None:
        """Read the version from a SKILL.md file's metadata, or None."""
        try:
            fm = self._parse_frontmatter(skill_md.read_text(encoding="utf-8"))
            raw_metadata = fm.get("metadata")
            if isinstance(raw_metadata, dict):

View on GitHub (pinned to 754d7323be)

Solutions

1. Ensure SKILL.md starts with `---` on the very first byte, ends the block with a second `---`, and uses LF line endings (`dos2unix SKILL.md`).
2. Install/upgrade the crewai SDK so the more robust `parse_frontmatter` is used instead of the strict regex fallback.
3. Remove any BOM: `sed -i '1s/^\xEF\xBB\xBF//' SKILL.md`.

Example fix

# before

---
name: x
---
(body)

# after
---
name: x
---
(body)

from pathlib import Path
import re

def frontmatter_block_at_start(path: str = "SKILL.md") -> bool:
    raw = Path(path).read_bytes()
    if raw.startswith(b"\xef\xbb\xbf"):
        return False  # BOM breaks the regex
    return bool(re.match(rb"^---\n.*?\n---", raw, re.DOTALL))

When it happens

Trigger: Calling `_parse_frontmatter` (via `crewai skill publish`) on a SKILL.md that does not begin with `---\n`; a UTF-8 BOM before the first `---`; Windows CRLF line breaks; or frontmatter delimiters written as `----`. The SDK parser is bypassed only when the crewai SDK package is absent.

Common situations: Files saved on Windows with CRLF; editors that insert a BOM; manually authored SKILL.md missing delimiters; older CLI installs without the SDK installed so the fallback path runs.

Related errors

• Failed to parse SKILL.md frontmatter: {exc}
• SKILL.md frontmatter must include a 'name' field.
• SKILL.md frontmatter must include a 'version' field before p
• Unable to read --definition path {definition_path}: {exc}
• Directory {skill_dir} already exists.

AI-assisted analysis of crewAIInc/crewAI@754d7323be (2026-08-15). Data as JSON: /api/errors/e9fdd82e2214d72f. Report an issue: GitHub.