Claude Code Frontmatter

VSCode extension — validation, autocomplete, and hover docs for Claude Code primitive file frontmatter.

Features

• Real-time validation — red squiggles on unknown or invalid frontmatter fields
• Autocomplete — Ctrl+Space lists valid fields and enum values inside frontmatter blocks
• Hover documentation — field descriptions, types, and required/optional status

Works on any .md file matching a Claude Code primitive path. No configuration needed.

Install

VS Code Marketplace:

ext install TheodrosYimer.claude-code-frontmatter

From VSIX (GitHub Releases):

code --install-extension claude-code-frontmatter-*.vsix

Supported primitives

What the extension catches

Prevent prettier from breaking skill discovery

If prettier reformats a single-line description into a multiline YAML string, Claude Code silently stops discovering the skill (#9817).

Add this to your global ~/.prettierrc:

{
  "overrides": [
    {
      "files": [
        "**/SKILL.md",
        "**/.claude/agents/*.md",
        "**/.claude/commands/*.md",
        "**/.claude/rules/*.md",
        "**/.claude/output-styles/*.md"
      ],
      "options": {
        "proseWrap": "preserve"
      }
    }
  ]
}

Disable VS Code's built-in Skill language validation

VS Code 1.112+ includes built-in Agent Skills support that assigns a "Skill" language to SKILL.md files with its own frontmatter validation. Its schema is incomplete — it flags valid Claude Code fields like allowed-tools, hooks, model, and effort as unsupported.

To override the "Skill" language and let this extension handle validation, add to your VS Code user settings (Cmd+Shift+P → "Open User Settings (JSON)"):

{
  "files.associations": {
    "**/SKILL.md": "markdown"
  }
}

Development

pnpm install        # install dependencies
pnpm build          # bundle with tsdown → dist/extension.cjs
pnpm test           # run vitest
pnpm test:e2e       # run VSCode integration tests
pnpm watch          # dev mode
pnpm package        # build + create .vsix
pnpm release        # release-it (requires VSCE_PAT)

CI runs on push to main via GitHub Actions. Conventional commits drive changelog generation.

License

MIT