MIME Type Lookup — File Extension to MIME Type

MIME (Multipurpose Internet Mail Extensions) type is a standard label that identifies the format of a file. It consists of a type and subtype: 'application/pdf', 'image/png', 'video/mp4'. Web servers use MIME types in the Content-Type header to tell browsers how to handle files. Without correct MIME types, browsers may download files instead of displaying them, or block them entirely.

File extensions (.pdf, .jpg) are part of the filename — they can be changed or faked. MIME types are metadata sent by the server in HTTP headers — they describe the actual content format. Security-conscious applications check both: the extension for user-facing display, and the MIME type (or magic bytes) for actual content validation. Our MIME database shows both for each format.

In Nginx: add_header Content-Type application/pdf. In Express.js: res.setHeader('Content-Type', 'image/png'). In Apache: AddType image/avif .avif. Most web frameworks auto-detect MIME types, but you should explicitly set them for: new formats (AVIF, WOFF2), file downloads (Content-Disposition: attachment), and API responses (application/json).

Magic bytes (file signatures) are the first few bytes of a file that identify its format — regardless of the file extension. For example, JPEG files always start with FF D8 FF, PNG with 89 50 4E 47. Security tools use magic bytes to detect extension spoofing (e.g., a .pdf file that's actually a JPEG). Our table shows magic bytes for each format.

application/octet-stream is the default fallback MIME type — it means 'unknown binary data'. Your web server isn't configured with the correct MIME type for that file extension. Fix: add the correct AddType directive (Apache), types block (Nginx), or Content-Type header (code). Use our lookup table to find the correct MIME type for any extension.