Glossary changedglossary
Nearest release: v2.1.280, published an hour before upstream edited the page. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.
Upstream edited this page at 22 Sep 2026 17:25 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 22 Sep 2026 17:37 UTC.
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## F ### Frontmatter
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151151Learn more: [Use extended thinking](/docs/en/model-config#extended-thinking)
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153## F
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155### Frontmatter
156
157A block of YAML settings at the very top of a Markdown file, between an opening `---` line and a closing `---` line. Skills, subagents, output styles, and rules each read their configuration from frontmatter, such as a skill's `description` or a subagent's `tools`, and treat everything after the closing `---` as the instructions. The opening `---` must be the file's first line. Each file type accepts its own set of fields.
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159Learn more: [Skill frontmatter](/docs/en/skills#frontmatter-reference), [Subagent frontmatter](/docs/en/sub-agents#supported-frontmatter-fields), [Output style frontmatter](/docs/en/output-styles#frontmatter), [Rule frontmatter](/docs/en/memory#rules-frontmatter-reference)
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153161## H
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155163### Hook
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