MIME Type Lookup

MIME (Multipurpose Internet Mail Extensions) types identify the format of a file or data transmitted over the internet. Servers send them in Content-Type headers so browsers know how to handle the response - whether to render a page, show an image, or trigger a download.

Some formats evolved over time (e.g. .js was once application/javascript but is now text/javascript). Others are generic containers (e.g. .ogg can be audio, video, or application). Always check the IANA registry for the current official type.

Both are used for JavaScript files. Historically this was application/javascript, but text/javascript became the de facto standard and is now the recommended MIME type in RFC 9239. Most browsers accept either, but text/javascript is preferred for modern development.

octet-stream is the generic 'unknown binary' fallback. When a server can't determine a file's MIME type, it sends octet-stream, and browsers typically trigger a download. It's also intentionally used to force file downloads instead of inline viewing — add a Content-Disposition header for the filename.

When uploading files via multipart/form-data, each part includes a Content-Type header with the file's MIME type. The server uses this to validate accepted file types. Never trust the client-provided MIME type alone — always verify file contents server-side using magic bytes or content inspection.

In Apache, use AddType in .htaccess. In Nginx, use the types directive. In Express.js, use res.type(). In all cases, ensuring correct MIME types improves browser compatibility, security (correct script execution), and download behavior.