What is a MIME type?
A MIME type is a two-part label — like image/png or application/pdf — that tells software what kind of content it has just received. Where a file extension is a hint for your desktop, a MIME type is the hint used on the internet.
How it's put together
Every MIME type has a general type, a slash, and a specific subtype. In image/png, "image" is the family and "png" is the exact format. Common families are text, image, audio, video, and application (the catch-all for everything else).
- text/plain — an ordinary .txt file
- text/csv — a comma-separated spreadsheet export
- application/pdf — a PDF document
- application/zip — a compressed archive
- application/octet-stream — "unknown binary data", the shrug of MIME types
Where you'll bump into one
Web servers attach a MIME type to every file they send, which is how your browser knows whether to display a page, show a picture, or offer a download. Email attachments use the same system — MIME literally stands for Multipurpose Internet Mail Extensions. Upload forms often accept or reject files by MIME type.
MIME type vs. file extension
They describe the same thing for different audiences. The extension travels with the filename on your computer; the MIME type travels with the file over a network. They can disagree — a misconfigured server may send a .pdf as application/octet-stream, which is why a PDF sometimes downloads instead of opening in the browser.
Where the registry records one, we show the MIME type on each extension page.