Exposing MyST and Document Metadata

When you build websites with MyST, there are two special kinds of metadata that get bundled with your MyST site. Each is explained below.

Page document metadata as .json¶

All webpages built with MyST come bundled with a .json representation of their content. This is a machine-readable version of the page that contains all of the metadata and page structure defined by the MyST specification.

You can access the MyST .json representation of a page by adding .json to the page name.

For example, the URL of this page is:

https://mystmd.org/guide/web-metadata

and you can access its JSON representation at the following URL:

https://mystmd.org/guide/web-metadata.json

MyST cross-reference data with myst.xref.json¶

When you create a MyST project on the web, all references in your MyST site are listed in a file that can be referenced by other projects using External References. This allows for programmatic reading of all MyST identifiers in a project (e.g. unique labels and the URL to which each resolves).

This is served in a file called myst.xref.json at the website root, and provides a list of reference links in JSON. For example, the cross-references file for the MyST Guide is at this location:

https://mystmd.org/guide/myst.xref.json

Below is an example structure of this file:

{
  "version": "1",
  "myst": "1.2.0",
  "references": [
    {
      "kind": "page",
      "data": "/index.json",
      "url": "/"
    },
    {
      "identifier": "xref-features",
      "kind": "heading",
      "data": "/index.json",
      "url": "/",
      "implicit": true
    }
  ]
}

The myst.xref.json data structure has three entries:

version

The version of the myst.xref.json schema

myst

The version of mystmd CLI that created the myst.xref.json data

references

A list of references that are exposed by the project, each object includes:

identifier

The identifier in the project for this reference, this will be unique in the project unless there is an implicit flag.

This is only optional for pages, which may not have identifiers. All other content must have an identifier.

html_id

The identifier used on the HTML page, which is stricter than the identifier.

This is only included if it differs from the identifier.

kind

The kind of the reference, for example, page, heading, figure, table.

data

The location of where to find the content as data. Use this link to find information like the reference’s enumerator, title or children.

The URL is relative from the location of where the myst.xref.json is served from.

url

The location of the HTML page; the URL is relative from the location of where the myst.xref.json is served from.

For constructing specific links to HTML pages, use <url>#<html_id || identifier>.

implicit

A boolean indicating that the reference is implicit to a page. This is common for headings, where the page information must be included.

Ensure your document is referenceable with CORS¶

To allow other MyST sites to reference your document, allow Cross-Origin Resource Sharing (CORS) from all origins (by setting Access-Control-Allow-Origin: *). This is on by default with GitHub Pages, but may not be enabled if you use a different provider (like Netlify).

Enabling all origins in CORS enables your site to:

• Support MyST cross-references (e.g., xref links, see docs) from other sites that use your website as a citation source.
• Enable content embedding, linking, or automated metadata access (e.g., for previews or API consumers) without authentication or same-origin constraints.

For an example of what it looks like to update CORS settings, see this GitHub PR updating CORS settings for Netlify.

What is CORS and why is it needed?¶

CORS is a browser security feature that restricts how resources on a web page can be requested from another domain outside the one that served the web page. For example, JavaScript running on external-site.org cannot fetch metadata or assets from https://book.the-turing-way.org/ unless explicitly allowed.

By setting CORS headers to allow all origins (*), you make it possible for external tools and sites to:

• Reference your content directly via structured and stable links.
• Preview or embed sections of your site from another page (with attribution).
• Use it in federated, cross-site knowledge systems (like MyST Markdown references in external books or educational hubs).

If your MyST site is public and does not require authentication, allowing all origins does not pose a security risk.