Front matter

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 <url>/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status	experimental or beta or deprecated or proposed or accepted or rejected or superseded		Lifecycle of the page.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.