Allow content-negotiation for POST requests too

Describe the problem

I want to do a +server.ts with a POST handler that downloads a file (a JSON backup).

And I want it to be accessible without client-side javascript:

<!-- backup/+page.svelte -->
<form method="POST" action="/backup">
  <input type="submit">
</form>

// backup/+server.ts

export const POST = () => {
  return new Response(JSON.stringify('{}'), {
    headers: {
      'Content-Type': 'application/json',
      'Content-Disposition': 'attachment; filename="backup.json"'
    }
  })
}

Unfortunately, there is a 405 error message with the message:

POST method not allowed. No actions exist for this page

This, despite the lack of +page.server.ts / actions.

Describe the proposed solution

When there is no actions for a page, allow the POST from the native browser form to hit +server.ts's POST handler.

This would be consistent with the GET behavior.

Alternatives considered

Currently, workarounds are using client-side javascript, or redirecting to a GET page in the action's handler.

A possible alternative feature is allow downloading files in an action handler.

Importance

nice to have

Additional Information

No response

The content negotiation seems to be working as intended, but our route handling logic doesn't check if any actions exist first before skipping past our endpoints.

On a side note, this is what the accept header look like for a native form submission request:

text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7

I've got the same exact bug, fully reproed here:

https://github.com/Crisfole/svelte-kit-bug-demo-repo

still reproducible on main, and the underlying gap is also present on version-3.

version-3 already fixed this exact class of bug for GET/HEAD in #16125, adding a check that falls back to the page when the endpoint can't actually serve the request:
https://github.com/sveltejs/kit/blob/4674301528/packages/kit/src/runtime/server/respond.js#L638-L647

that check is scoped to method === 'GET' || method === 'HEAD' only, so POST still goes straight to the endpoint via is_endpoint_request() with no check for whether it has a POST handler, and no fallback to the page's actions. was POST left out on purpose, or just not gotten to yet? if it's the latter, i'll extend the same endpoint_can_handle check to POST and open a PR against main.

fix: fall back to page actions when a sibling endpoint has no POST ha…

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Allow content-negotiation for POST requests too #10863

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Allow content-negotiation for POST requests too #10863

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Describe the problem

Describe the proposed solution

Alternatives considered

Importance

Additional Information

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teemingc commented on Oct 12, 2023

Crisfole commented on Sep 4, 2025

Bishwas-py commented on Jul 14, 2026

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