SKILL.md Frontmatter — All Knobs

~16 min · skills, frontmatter, yaml, config

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The YAML head is the contract

A Skill's frontmatter declares everything the host AI needs to load it correctly: identity, when to invoke, what arguments, which support files, which model. Body is the prompt; frontmatter is the wiring.

The eight fields that matter: name (kebab-case identifier, becomes /name), description (what + when, used by auto-invocation), invocation (explicit / auto / disabled), arguments (named args, accessible as {{name}}), paths (extra files loaded into context), model (override host's default), subagent (run isolated), and the implicit version from your VCS.

Code

Frontmatter with every relevant field·markdown

---
name: security-audit
description: |
  OWASP-aware security audit of a file or directory.
  Auto-invoke when user mentions "security", "vulnerability",
  or asks about auth/payments/data-handling code.
invocation: auto
arguments:
  - name: target
    description: File or directory to audit
    required: true
  - name: severity_floor
    description: Lowest severity to include (low | medium | high)
    required: false
    default: low
paths:
  - checklists/owasp-top10.md
  - templates/finding.md
model: claude-opus-4-7
subagent: true
---

Substitution and references in the body·markdown

You are a senior application security engineer.

Audit {{target}}. Use checklists/owasp-top10.md as the floor.
For each finding:
- Severity (CVSS 3.1)
- File:line citation
- CWE class
- Remediation snippet

Filter to severity >= {{severity_floor}}.
Format each finding using templates/finding.md.

External links

SKILL.md frontmatter reference

Exercise

Take an existing Skill (yours or one of the bundled ones) and add three frontmatter fields it doesn't already use: at least one arguments entry, at least one paths entry, and a meaningful description. Verify auto-invocation triggers when you'd expect.

Progress

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