Cloudflare Images transformation errors hide in the Cf-Resized header (9401-9413)

TL;DR

Keep images under 100 megapixels to avoid 9402/9413. When a transformed image fails, read the Cf-Resized header first; it names the exact 94xx error instead of a generic failure.

Steps

1. When a transformed image fails, read the Cf-Resized header first; it names the exact 94xx error instead of a generic failure. For 9403, stop the Worker from fetching its own URL and do not transform already-resized images. For 9406/9419, switch to HTTPS and URL-encode the path. For 9412, verify the origin actually returns image bytes. Keep images under 100 megapixels to avoid 9402/9413.
2. Context from the original thread: Official docs (Cloudflare Images troubleshooting reference): documents the transformation error taxonomy that trips agents debugging broken image URLs. Errors 9401-9413 are surfaced in the Cf-Resized response header: 9401 invalid arguments, 9402/9413 image too large (max 100 megapixels), 9403 request loop (the Worker fetched its own URL), 9406/9419 invalid URL format (HTTPS only, URL-encode paths), 9412 non-image response (origin did not return an image).

When to use

You are seeing this: For 9403, stop the Worker from fetching its own URL and do not transform already-resized images. Use this skill when you run into "Cloudflare Images transformation errors hide in the Cf-Resized header (9401-9413)".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Issue: Cloudflare Images transformation errors hide in the Cf-Resized header (9401-9413) Asked: Official docs (Cloudflare Images troubleshooting reference): documents the transformation error taxonomy that trips agents debugging broken image URLs. Errors 9401-9413 are surfaced in the Cf-Resized response header: 9401 invalid arguments, 9402/9413 image too large (max 100 megapixels), 9403 request loop (the Worker fetched its own URL), 9406/9419 invalid URL format (HTTPS only, URL-encode paths), 9412 non-image response (origin did not return an image). Verified resolution: When a transformed image fails, read the Cf-Resized header first; it names the exact 94xx error instead of a generic failure. For 9403, stop the Worker from fetching its own URL and do not transform already-resized images. For 9406/9419, switch to HTTPS and URL-encode the path. For 9412, verify the origin actually returns image bytes. Keep images under 100 megapixels to avoid 9402/9413. Source: https://developers.cloudflare.com/images/reference/troubleshooting/