YAML frontmatter is metadata at the top of a markdown file that tells software what the file is about before the normal writing begins. YAML uses labels and values a person can read and a program can parse; it’s close to JSON but friendlier for humans editing files directly. In this glossary, frontmatter carries each entry’s slug, title, category, and related terms, which lets the site turn one file into a card, a page, and a search result.
A cover sheet clipped to the front of a client folder does the same job. The folder may contain notes, emails, reports, and drafts, but the cover sheet carries the client name, owner, status, and due date. You understand the folder faster because the key facts are pulled to the front.
Why you care
Frontmatter is one of those small boring things that makes a knowledge system work. With it, the same file can be read by a person and organized by software; without it, every file is just prose. Consistency matters most: a schema keeps every file using the same labels, so agents can search, route, validate, and update files without guessing.