The front matter keys the engine reads. Every key is optional; an unknown key is kept and passed to the layout, never rejected. Front matter is a YAML block between two `---` lines at the top of a `.md` or `.html` file. A page without front matter still builds: its title is its first `h1`, its URL comes from its file path, and its layout comes from `defaults` in `mizzen.yml` or from the theme. ## Keys the engine reads | Key | Type | Allowed | What the engine does with it | | --- | --- | --- | --- | | `agent` | object | keys `edit`, `notes`, `source` | Instructions for agents that edit this page. | | `canonical_url` | string | `^(/\|https://)[^\s"<>]*$` | The original URL of the page if it was first published elsewhere; the canonical link and `og:url` use it. | | `description` | string | | One sentence for the meta description, the `llms.txt` entry, and the search excerpt. | | `dir` | `ltr` or `rtl` | | Text direction. Unset, it comes from the page's `lang`. | | `image` | string | `^(/\|https://)[^\s"<>]*$` | The page's social image: a path on this site or an `https` URL. `og:image` uses it. | | `lang` | string | `^[a-z]{2,3}(-[A-Za-z0-9]{2,8})*$` | Language of the page as a BCP 47 tag, such as `en` or `fa`. Unset, it comes from the language prefix of its folder, then from `lang` in `mizzen.yml`. | | `last_modified_at` | string | `^\d{4}-\d{2}-\d{2}([ T]\d{2}:\d{2}(:\d{2}(\.\d+)?)?( ?(Z\|[+-]\d{2}:?\d{2}))?)?$` | The date the page last changed; the page's `/index.json` reports it as `lastModified`. | | `layout` | string | not empty | The theme layout that renders the page. Unset, it comes from `defaults`, then the theme's default layout. An unknown name is an error. | | `og` | boolean | | `false` drops the page's Open Graph and Twitter card tags and the image in its structured data. | | `order` | number | | Sort order among siblings in navigation built from folders. Pages without it follow, sorted by title. | | `permalink` | string | `^/` | The output URL, a path starting with `/`. Unset, the URL comes from the file path: `guide/install.md` and `guide/install/index.md` both give `/guide/install/`. | | `published` | boolean | | `false` keeps the page out of the build. | | `redirect_from` | string or list of strings | | Old paths that redirect to this page. | | `redirect_to` | string | | A path on the site or an `https` URL this page redirects to; its body is not rendered. | | `search` | boolean | | `false` leaves the page out of the search index. | | `sitemap` | boolean | | `false` leaves the page out of `sitemap.xml`. | | `status` | `experimental` or `beta` or `deprecated` or `proposed` or `accepted` or `rejected` or `superseded` | | Lifecycle of the page. The engine checks the value; the theme decides how to show it. | | `title` | string | not empty | Page title. Without it, the first `h1` of the body; without that, the file name. | | `translation_key` | string | not empty | Links a page to its translations. Use the same key on every translation. | | `updated` | string | `^\d{4}-\d{2}-\d{2}([ T]\d{2}:\d{2}(:\d{2}(\.\d+)?)?( ?(Z\|[+-]\d{2}:?\d{2}))?)?$` | The date the page was last substantially edited; `sitemap.xml` uses it as `lastmod`. | ## Folder defaults `defaults` in `mizzen.yml` sets front matter for every page under a folder, such as `layout` for all of `docs/`. A key in a page's own front matter always wins over `defaults`.