Very early stage work in progress!!

MDS is a tiny language for describing how Markdown should look. With mdvalidate, you write schemas that define a shape of Markdown, and MDS checks real documents against them.

It's designed for validating a stream of Markdown via stdin, so you can pipe input (like LLM output) and validate the shape of its response.

mdvalidate schemas consist of many "matcher" patterns, and all matchers have labels. This means that all validated markdown files can produce a JSON of matches found along the way.

We plan to eventually support converting a Markdown schema into a JSON schema describing the shape of the output that it produces once it has validated some Markdown file.

mdvalidate is written in 100% safe rust and is 🔥 blazingly fast 🔥.

• Literal Matching: Regular Markdown stays literal — if it says # Title, it must match exactly.
• Matchers: Use `label:/regex/` to define rules for dynamic content.
• Optional or Repeated Items: Add ? for optional things, + for one or more.
• Lists & Sublists: Validate nested lists with pattern control.
• Escaping: Add ! to disable regex interpretation — great for examples.

Here’s a simple schema that will validate all grocery lists of a specific shape.

# Grocery List

- `item:/[A-Z][a-z]+/`+         <!-- one or more items; each starts with a capital letter -->
  - `note:/\w+/`?{,2}           <!-- up to two optional sub-notes per item -->

A passing document:

# Grocery List

- Apples
  - organic
  - local
- Bananas
  - ripe

A failing document (too many sub-notes):

# Grocery List

- Apples
  - organic
  - local
  - green

You can build mdvalidate with the nix build system using nix build github:404wolf/mdvalidate.

You can build our design document or software requirements specification with typst, using

typst compile docs/design_document.typ
typst compile docs/software_requirements_specification.typ

By Wolf Mermelstein and Alessandro Mason.