Storefront returns 404 for product and collection pages when requested with Accept: text/markdown

Agentic Commerce
1

Hi all, thanks for the recent agent-commerce work (UCP, agents.md, Agentic Storefronts). While testing how AI agents see our store, we found what looks like a platform-level bug in how the storefront answers markdown requests. Shopify Support reviewed it and suggested posting here so the right engineering team sees it.

Store: shazu.com (Online Store, Liquid theme, no apps that touch requests)

What happens

  1. Product and collection pages return 404 when markdown is requested, even when HTML is listed as a fallback. Only a pure text/html request works.
  2. The homepage labels its response as markdown but sends HTML. It returns Content-Type: text/markdown, but the body is the normal HTML page.

Reproduce

curl -s -o /dev/null -w "%{http_code} %{content_type}\n" \
  -H "Accept: text/markdown" \
  https://shazu.com/products/pink-conch-shell-bracelet-soft-tide
URL Accept Result
/products/pink-conch-shell-bracelet-soft-tide text/markdown 404 text/plain, body “Not Found”
/products/pink-conch-shell-bracelet-soft-tide text/markdown, text/html;q=0.9 404 text/plain
/products/pink-conch-shell-bracelet-soft-tide text/html 200 text/html
/collections/bracelet text/markdown 404 text/plain
/ (homepage) text/markdown 200 text/markdown, but the body starts with <!doctype html>

To run it in a browser: https://reqbin.com/labyixg3 opens the product request with Accept: text/markdown. Click Send.

Request IDs from 2026-09-26 00:41:09 UTC, in case they help find it in the logs:

  • text/markdown → 404: e306e3e2-6af7-430d-9616-b262764617a7-1790383269
  • text/markdown, text/html;q=0.9 → 404: ad4870ed-af03-4b03-bd4f-f100fb9df4b7-1790383269
  • text/html → 200: b983ae2c-dae8-493a-a581-c191c77d622d-1790383269

It doesn’t seem to be store-specific

Our theme has no code that handles the Accept header. On another Shopify store (allbirds.com), a markdown request for /products/mens-tree-runners redirects (301) to a collection page, which then returns 404. A text/html request for the same product returns 200.

Why it matters

Some AI agents and coding tools ask for markdown first, with HTML as a fallback. On a Shopify store right now, they get a 404 for every product and collection page, so the products look like they don’t exist. /agents.md itself is served correctly.

What we’d expect

Either a real markdown version of the page, or, when markdown isn’t available, the normal HTML response (or a 406), not a 404. The homepage’s Content-Type should match what’s actually in the body.

Happy to test anything that would help. Thanks!

Shazu (shazu.com)

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