What is MIME type "application/octet-stream"?

A MIME type is a string that tells browsers and other tools how to handle a particular kind of file.

application/octet-stream is a generic MIME type that signals raw binary data. It tells systems that the file may not have a dedicated viewer or processor.

When a browser or email client sees this type, it usually prompts you to download the file rather than open it directly. This prevents potential security risks because the data isn’t assumed to be safe for inline rendering.

Main Purpose: To denote files that consist of unformatted binary streams.
Common Uses: Files that lack a more specific MIME type fall back to this. It appears in downloads, email attachments, and software package transfers.
Fallback Role: It is used when a file’s true format isn’t known. Many different file types use it as a default marker.

This MIME type is often used by many file formats. For example, a file could be a binary package like an ZIP archive or an executable such as an EXE file.
It can also cover media files like MOV or MP4, images such as JPG, PNG, and even data files like DAT or BIN.

Other file types—including PDF, TXT, XML, JSON, STL, and even specialized formats like an APK—may be served with this MIME type if no more precise designation exists.

This wide usage stems from its versatility. Software and servers choose application/octet-stream to safely deliver files whose nature is undetermined.

Learn more about MIME types on MDN.

Associated file extensions

.pdf, .zip, .jpg, .png, .svg, .mov, .dat, .txt, .xml, .json, .mp4, .exe, .bin, .gz, .x, .stl, .rpa, .tif, .dmg, .iso, .dmp, .mkv, .step, .apk, .dll, .bmp, .pub, .tiff, .mb, .msg, .aae, .bak, .ics, .db, .mpp, .md, .ini, .key, .ds_store, .raw, .max, .sav, .wps, .xls, .php, .dms, .box, .dav, .cad, .cbr, .prn

Usage Examples

HTTP Header

When serving content with this MIME type, set the Content-Type header:


    Content-Type: application/octet-stream

HTML

In HTML, you can specify the MIME type in various elements:


    <a href="file.dat" type="application/octet-stream">Download file</a>

Server-side (Node.js)

Setting the Content-Type header in Node.js:


    const http = require('http');
    
    http.createServer((req, res) => {
      res.setHeader('Content-Type', 'application/octet-stream');
      res.end('Content here');
    }).listen(3000);

Associated file extensions

FAQ

What is a MIME type?

A MIME (Multipurpose Internet Mail Extensions) type is a standard that indicates the nature and format of a document, file, or assortment of bytes. MIME types are defined and standardized in IETF's RFC 6838.

MIME types are important because they help browsers and servers understand how to process a file. When a browser receives a file from a server, it uses the MIME type to determine how to display or handle the content, whether it's an image to display, a PDF to open in a viewer, or a video to play.

MIME types consist of a type and a subtype, separated by a slash (e.g., text/html, image/jpeg, application/pdf). Some MIME types also include optional parameters.

How do I find the MIME type for a file?

You can check the file extension or use a file identification tool such as file --mime-type on the command line. Many programming languages also provide libraries to detect MIME types.

Why are multiple MIME types listed for one extension?

Different applications and historical conventions may use alternative MIME identifiers for the same kind of file. Showing them all helps ensure compatibility across systems.