.bin MIME type

Content-Type: application/octet-stream. It's already compressed, so servers shouldn't gzip it.

application/octet-stream

Arbitrary binary data — the fallback type for anything without a more specific one.

Good to know

Browsers download application/octet-stream responses instead of displaying them.
Many servers use it as the default for unknown extensions; nginx's default_type sets it.
Under nosniff, a script or stylesheet served as application/octet-stream is blocked.

The response header to send:

Content-Type: application/octet-stream

Most servers pick the type from the file extension. If yours sends the wrong one, map it explicitly:

nginx (inside the types block in mime.types)

application/octet-stream bin;

Apache (.htaccess or server config)

AddType application/octet-stream .bin

Express

res.set("Content-Type", "application/octet-stream");

Python

import mimetypes

mimetypes.add_type("application/octet-stream", ".bin")

HTML file input

<input type="file" accept=".bin,application/octet-stream">

See what a server sends for a file, and what type a local file really is by its contents:

curl -sI https://example.com/file.bin | grep -i '^content-type:'
file --mime-type file.bin

application/octet-stream.

Content-Type: application/octet-stream. It's already compressed, so servers shouldn't gzip it.

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