MDS071: required-frontmatter

Every file in the configured glob scope must declare each named front-matter field with a present, non-empty value.

A file in scope is flagged once per required field that is absent, explicitly null, or empty. An empty string (including whitespace only), an empty list, and an empty map all count as empty; any other scalar — a non-blank string, a number, a boolean — satisfies the field. The rule checks presence, not a particular type. A file with no front matter at all is missing every required field.

The diagnostic anchors to the file’s first line. With no fields configured the rule reports nothing, so it ships registered and opt-in: nothing fires until a convention, kind, or config names the fields.

The canonical use is the Open Knowledge Format (OKF), where every concept document must carry a non-empty type and the reserved index.md and log.md files are excluded. The okf starter (mdsmith init --starter okf) scaffolds exactly that.

# Settings

Setting both field and fields is a config error. With no fields configured the rule is inert. Globs match the raw path, the cleaned path, and the base name, so exclude: [index.md] removes every index.md at any depth.

# Config

Require a non-empty type on every Markdown file except the OKF reserved files:

rules:
  required-frontmatter:
    fields: [type]
    exclude: [index.md, log.md]

Single field via the alias:

rules:
  required-frontmatter:
    field: type

Disable:

rules:
  required-frontmatter: false

# Examples

# Bad — the required field is missing

---
title: Orders
---

front-matter "type" is required but missing

# Bad — the required field is empty

---
type: ""
---

front-matter "type" is required but empty

# Good — the field is present and non-empty

---
type: BigQuery Table
title: Orders
---

# See also

• MDS069 — the cross-file companion: enforces that a field’s values are distinct across files, where this rule enforces that the field exists and holds a value
• MDS020 — validates front matter against a full schema (types, enums, sections); reach for it when a presence-and-non-empty check is not enough
• OKF guide — authoring and validating Open Knowledge Format bundles with mdsmith

# Meta-Information

• ID: MDS071
• Name: required-frontmatter
• Status: ready
• Default: disabled (opt-in)
• Fixable: no
• Implementation: source
• Category: structural