Type an extension or a MIME type to filter a reference table of common file formats, their content types and what each format is.
A MIME type (also called a media type or content type) is the label a server sends with a file so a browser knows how to handle it — display it, download it, or hand it to another program. The table lists common extension and MIME pairings with a one-line description of each format. Filtering happens against the built-in table on this page; an extension with no entry reports no match rather than a guess, and some formats legitimately have more than one registered type.
What is a MIME type used for? It tells the receiving program what a file actually is, independent of its name. A server sending image/png with a picture lets the browser display it as an image; application/octet-stream instead tells the browser to treat the bytes as a generic download.
Why can one extension have several MIME types? Some types were registered at different times or by different vendors, and a few extensions cover more than one format. The table lists the most common current pairing for each extension.
What if an extension shows no match? It is not in the reference table of common formats on this page. That does not mean the format is invalid — only that it is less common or specialised.