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310310### Frontmatter reference
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312Beyond the markdown content, you can configure skill behavior using YAML frontmatter fields between `---` markers at the top of your `SKILL.md` file:
312Configure a skill with YAML [frontmatter](/docs/en/glossary#frontmatter) between `---` markers at the top of `SKILL.md`, and write the skill's instructions as Markdown after the closing `---`. Field names use lowercase words separated by hyphens, except `when_to_use`. A [command file](#where-skills-live) in `.claude/commands/` accepts the same fields except `name` and `paths`. This example sets four fields:
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314314```yaml theme={null}
315315---
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322322Your skill instructions here...
323323```
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325All fields are optional. Only `description` is recommended so Claude knows when to use the skill.
325All fields are optional. Only `description` is recommended so Claude knows when to use the skill. A field name must match the table exactly, hyphens included: Claude Code ignores a field it doesn't recognize without reporting an error.
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327Claude Code reads the frontmatter only when the opening `---` is the file's first line. Otherwise it treats the whole file, `---` markers included, as skill content.
327Claude Code reads the frontmatter only when the opening `---` is the file's first line. Otherwise it treats the whole file, `---` markers included, as skill content. If the YAML between the markers doesn't parse, the skill still loads with no fields set; see [Skill not triggering](#skill-not-triggering) to find and fix the error.
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329329Boolean fields accept `yes`, `no`, `on`, `off`, `1`, and `0` in any letter case, in addition to `true` and `false`. Before v2.1.218, Claude Code recognized only `true` and `false`.
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