What is MIME type "application/x-ms-mst"?

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

application/x-ms-mst is a MIME type for Windows SDK Setup Transform scripts.
These scripts adjust installation settings and tailor how a package installs.
They are used with the file type MST.
The transform script holds instructions that change options during installation. It is a tool in the Windows SDK environment that helps streamline software deployment and enhance user experience. External details on similar file types can be found at Filext.

Associated file extensions

.mst

Usage Examples

HTTP Header

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


    Content-Type: application/x-ms-mst

HTML

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


    <a href="file.dat" type="application/x-ms-mst">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/x-ms-mst');    
      res.end('Content here');    
    }).listen(3000);

Associated file extensions

.mst

FAQs

What is the primary purpose of an MST file?

An MST file is a Windows Installer Transform used to customize the installation of an MSI package. It acts as a "diff" file, applying specific changes—such as language settings or feature selections—to the main installer database during deployment.

How do I configure IIS to serve application/x-ms-mst?

Microsoft IIS may not serve this file type by default, resulting in 404 errors. To fix this, add a MIME map in your web.config or IIS Manager with the extension .mst and the content type application/x-ms-mst.

Can I edit an MST file with a text editor?

No, MST files are binary databases, not plain text scripts. To create or modify them, you must use specialized tools like Microsoft Orca (included in the Windows SDK) or third-party MSI editors.

How do I apply an MST transform via the command line?

You can apply the transform when running the main installer by using the TRANSFORMS property. The command typically looks like: msiexec /i setup.msi TRANSFORMS=custom.mst.

Why does the MIME type start with x-ms-?

The prefix x- denotes a non-standard or experimental type, while ms indicates it is proprietary to Microsoft. This specific string signals to the browser or server that the file is a Microsoft-specific transform script.

Are application/x-ms-mst files safe to open?

These files contain instructions that modify software installation and system settings. You should only use MST files from trusted administrators or vendors, as a malicious transform could compromise the security of the installed software.

General 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.