Extension ↔ MIME Type Converter

Side Note — Where MIME types came from

MIME (Multipurpose Internet Mail Extensions) was devised in the early 1990s to let email carry images, audio, and other binary attachments. Email at the time was built on a text-only standard (RFC 822) that assumed plain ASCII, so binary data had to be encoded (typically with Base64) and tagged with a label describing what kind of data it actually was — that label is the MIME type.

A MIME type is written as "type/subtype" (for example, image/png). The type is a broad category — image, audio, video, text, application, and so on — while the subtype names the specific format. This two-level design lets the system grow simply by registering a new subtype whenever a new format appears, without redesigning the whole scheme.

MIME types soon moved beyond email into HTTP, where they became the standard way a web server tells a browser, via the "Content-Type" response header, how a file should be interpreted. Browsers rely on this header as much as (often more than) the file extension, so a misconfigured Content-Type on the server can make a correctly-named file behave unexpectedly — triggering a download instead of rendering, or refusing to execute a script.

Today the IANA (Internet Assigned Numbers Authority) is the official registry for MIME types, and new media types go through a formal registration process. That said, the mapping between file extensions and MIME types is not itself something IANA enforces — a lot of it is convention built up in practice — which is exactly why a reference table like this one is useful.