# .msi MIME Type: application/x-msi

> Windows Installer packages. No type is registered; application/x-msi is the common one.

- MIME type: `application/x-msi`
- Extensions: .msi
- Also seen as: `application/x-msdownload`
- Content-Type header: `application/x-msi`
- Compress in transit: no (already compressed)
- File signature: `D0 CF 11 E0 A1 B1 1A E1` (the OLE2 compound-file signature shared by legacy Office formats)

## Good to know

- MSI files share the OLE2 signature with legacy Office documents, so the first bytes alone don't identify them.
- Like `.exe` downloads, they carry the Mark of the Web and trigger SmartScreen warnings unless signed.

## Server configuration

### nginx (inside the types block in mime.types)

```
application/x-msi msi;
```

### Apache (.htaccess or server config)

```
AddType application/x-msi .msi
```

### Express

```
res.set("Content-Type", "application/x-msi");
```

### Python

```
import mimetypes

mimetypes.add_type("application/x-msi", ".msi")
```

### HTML file input

```
<input type="file" accept=".msi,application/x-msi">
```

## FAQ

### What is the MIME type for .msi files?

`application/x-msi`. You may also see `application/x-msdownload`, but `application/x-msi` is the one to send.

### What Content-Type header should a .msi file be served with?

`Content-Type: application/x-msi`. It's already compressed, so servers shouldn't gzip it.

### How can I tell if a file is really a .msi?

Check its bytes rather than the extension: MSI files start with `D0 CF 11 E0 A1 B1 1A E1` — the OLE2 compound-file signature shared by legacy Office formats. On the command line, `file --mime-type name.msi` does this for you.

## Related types

- [.exe — application/vnd.microsoft.portable-executable](https://www.devkult.com/mime/exe.md)
- [.bin — application/octet-stream](https://www.devkult.com/mime/bin.md)

Open the interactive page: https://www.devkult.com/mime/msi