A misconfigured Content-Type header is one of those bugs that doesn't announce itself. A PDF served as text/plain might download instead of preview. A JSON API response served as text/html can confuse a strict client parser. None of these produce a clear error message pointing at the header — they just look like "something's off."
The extension and the MIME type aren't the same thing
A file's extension is a hint for humans and some operating systems; the MIME type in the Content-Type header is what actually tells a browser or HTTP client how to interpret the bytes. Static file servers, CDNs and custom upload handlers all need the correct mapping configured somewhere, and it's easy for that config to drift or miss a newer format like .webp or .woff2.
Fonts and web assets are common gaps
Web fonts (.woff, .woff2), WebAssembly modules (.wasm) and some image formats are more recent additions to the MIME type space, and older server configs sometimes don't have correct entries for them — leading to fonts that silently fail to load or WASM modules that get rejected by strict browsers.
TeckForge's MIME Type Lookup is a quick, searchable reference — look up an extension to get its correct MIME type, or search by MIME type to confirm which extension it maps to, without digging through server documentation.
