MIME Type Lookup

Matching extensions to content types

A MIME type, or media type, is the label that tells software what kind of data a file holds, like image/png or application/json. It is sent in the HTTP Content-Type header and drives how a browser handles a response: render it, download it, or run it. A lookup maps a file extension to its canonical type, or searches types by keyword.

Why the server header wins

The file extension is a hint for humans; the Content-Type header is what the browser trusts. Serve a JSON file with text/plain and a fetch expecting JSON may refuse it. Serve a script with the wrong type and strict browsers block it. Getting the mapping right on your server avoids a long tail of "it works locally but not deployed" bugs.

Example

.json  -> application/json
.svg   -> image/svg+xml
.woff2 -> font/woff2
.wasm  -> application/wasm
.md    -> text/markdown

The structure of a type

A media type is type/subtype, optionally with parameters like ; charset=utf-8. The +xml and +json suffixes signal the underlying structure, so image/svg+xml is an image that is also XML. For text formats, declaring the charset prevents mojibake from a mis-guessed encoding.

FAQ

My .js file is served as text/plain, is that a problem? Yes for modules; browsers require a JavaScript type for type="module" scripts. Configure the server to send text/javascript.

Is there one correct type per extension? Mostly, but a few extensions have several registered types, and some types predate a formal registration, so lists can disagree at the edges.

Does the extension decide the type automatically? Only if your server is configured to map it. The extension itself carries no authority over the wire.