How to look up a MIME type
- Type a file extension such as
.webpordocx, part of a MIME type such asvideo/, or a word such as font. - Click a MIME type in the table to copy it.
- To identify an unknown file, drop it on the box. The first bytes (the file signature or "magic number") are checked, and the result is compared with the extension and what your browser reports, so renamed or mislabelled files are caught.
Why MIME types matter
A MIME type (or media type), such as image/png or application/json, tells browsers and other software how to handle data. Web servers send it in the Content-Type header, emails use it for attachments, and APIs use it to describe request and response bodies. A wrong type causes real problems: JavaScript modules served as text/plain are refused, fonts without the right type may be blocked, and downloads may open as garbled text in the browser.
When you configure a server or storage bucket (Nginx, Apache, Netlify, S3, Cloudflare R2), check that modern formats such as .webp, .avif, .woff2, .wasm and .webmanifest have the right types, as older defaults often miss them. For security, also send X-Content-Type-Options: nosniff so browsers do not guess types.
File detection reads only the first 32 bytes locally. Your file is not uploaded.
What MIME type should I use for unknown files?
application/octet-stream, which means arbitrary binary data. Browsers will usually offer to download it.
Is it text/javascript or application/javascript?
text/javascript. The HTML standard and RFC 9239 made it the official type; application/javascript still works but is considered legacy.
Why do DOCX and XLSX files show as ZIP?
Office Open XML documents are ZIP archives containing XML files, so their signature is the same as ZIP. The extension tells them apart.