What to run
Open MIME Type Lookup. It stays in the browser.
How to read the result
The type is the usual mapping for that extension.
Unknown means the table has no entry, not that the file is safe.
.jpg and .jpeg should both map to image/jpeg.
What to open next
Open HTTP Headers on a URL that serves the file, and compare content-type to the lookup. The header check runs from Cloudflare.