Concepts
A concept is a single unit of knowledge: one Markdown file with a YAML frontmatter block at the top and a Markdown body below it.
Official OKF specification requirement
Every non-reserved
.md concept file must be UTF-8 Markdown, begin with parseable YAML frontmatter, and declare a non-empty type field.type is free-form — OKF does not require a central taxonomy, and unknown or custom type values are always valid. See the Type Explorer for what types show up across a real bundle.
Official OKF specification requirement
Unknown YAML fields must be accepted and preserved. A tool must never strip a custom field merely because it doesn't recognize it.
Recommended, not required
title, description, resource, and tags are recommended for discoverability, but a concept missing any of them is still fully conformant.
OKF Tools recommendation
The Linter flags missing recommended fields as informational, never as errors — this distinction is enforced in the shared validation engine, not left to each tool to get right independently.