REST API sometimes returns HTML instead of JSON - is this intentional?

[FarooqAlaulddin]

REST API sometimes returns HTML instead of JSON - is this intentional?

Hey folks,

I'm running into inconsistency with plone.rest that's causing issues in my headless setup. Sometimes when I hit a non-existent API endpoint, I get a 404 JSON response, but other times I get HTML from the classic UI instead.

What's happening

Let's say I have a content item at /my-page and I make API calls to:

• /my-page/nonexistent → Returns JSON 404
• /my-page/edit → Returns HTML edit form

Looking at the code in traverse.py , I can see why this happens. When a REST service isn't found, there's this fallback:

if service is None:
    # No service, fallback to regular view
    view = queryMultiAdapter((self.context, request), name=name)
    if view is not None:
        return view
    raise

So if there's a browser view with that name (like /edit, /sharing, etc.), it returns the HTML view instead of a 404.

Why is this a problem?

I'm using Plone purely as a headless CMS. My frontend expects JSON from all API calls, so when it suddenly gets HTML, things break. I have to add extra error handling to check content types, which feels wrong.

My questions

• Is this fallback behavior intentional? I'm trying to understand why plone.rest was designed this way. Was it:
• Right now I'm monkey-patching the traverser to remove the fallback, but that's not ideal for maintenance.
• Anyone else hit this case? Am I missing something obvious here?
• Thoughts?

---

Environment:

• Plone 6.1.1
• Headless CMS setup with HTMX

[davisagli]

To be honest, I'm not sure why this fallback is there. I would like to remove it, but I'm a bit worried that it would break backwards compatibility with someone who is relying on it. I'd suggest adding a way to opt out of it with an environment variable, so that we can start to experiment and see if it causes any problems.

[aryandevash-jpg]

I want to look upon this issue, what is its current status?