Nothing is served at the .md URL

Work through these in order. The first three cover almost every report.

1. Is the content type enabled?

By far the most common cause. The plugin ships inactive: with no content type ticked under Settings → Markdown Alternate → General, every .md URL on the site returns 404. Tick at least one and save.

The same applies one type at a time: enabling Posts does nothing for a custom post type until that type is ticked too.

2. Is this particular post eligible?

A post is served only when it is published, carries no password, and uses the standard post format. Any of these returns 404 by design:

• a draft, pending, scheduled or private post;
• a password-protected post — including for a visitor who has already entered the password, because the rule is about the content, not the reader;
• a post whose format is aside, status, quote, link, image, video, audio, gallery or chat;
• a post rendered by a page builder — Bricks, Elementor, Divi, WPBakery, Oxygen, Beaver Builder or Breakdance. This is decided per post, from the builder’s own render mode, so a site whose pages use a builder keeps every article that does not. See Page builders.

A quick way to tell the difference between “not eligible” and “not working”: if the post were eligible, its HTML page would carry a Markdown alternate link. View source and search for text/markdown. Nothing there means the post is being excluded, not that the endpoint is broken.

3. Are you being blocked before WordPress?

If you are testing from the command line, check what actually came back before assuming it is the plugin:

curl -sI https://example.com/my-post.md

A 301 or 302 with a Location pointing at something like /WAF-BLOCKED is your firewall refusing the request, usually because curl is on a bad-bot list. It applies to the whole site — the HTML page is blocked identically. Re-test with a browser user agent:

curl -sI -A 'Mozilla/5.0' https://example.com/my-post.md

Some managed firewalls block specific AI crawlers by name as well. That is a policy decision on your host, separate from anything the plugin does.

4. Do you have pretty permalinks?

With plain permalinks (?p=123) there is no path to append .md to. The plugin falls back to ?format=markdown on the permalink and the settings page says so. Switch to a pretty structure under Settings → Permalinks for clean .md URLs.

5. Is another plugin answering first?

The endpoint runs early on template_redirect, but a redirect manager or a security plugin can act sooner and send a redirect before the plugin sees the request. If .md URLs redirect somewhere unexpected, test with other plugins deactivated to find which one owns the rule.

For /llms.txt specifically, a real file in the site root always wins: the web server delivers it without ever starting WordPress. The settings page flags this when it detects one.

Still nothing?

If the URL returns HTML rather than 404, the problem is different and usually a cache — see Markdown negotiation returns HTML.