What is MIME type "application/x-123"?

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

The MIME type application/x-123 is assigned to spreadsheet files created by Lotus 1-2-3 software. It signals to your system that the file holds spreadsheet data with formulas, cell styles, and structures.

This type is especially important for legacy file support. It works with older files created in different versions of the software. For example, files using the following extensions are identified by this MIME type: 123, WKS, WK1, and WK2.

Main use: To help software recognize and correctly open Lotus 1-2-3 spreadsheets.
Legacy data handling: It aids modern applications in importing, converting, or archiving these older file formats.
File management: Operating systems and email programs use this type to safely process file attachments and data.

For more technical details on MIME types, see the information available at MIME on Wikipedia.

Associated file extensions

.123, .wks, .wk1, .wk2

Usage Examples

HTTP Header

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


    Content-Type: application/x-123

HTML

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


    <a href="file.dat" type="application/x-123">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-123');
      res.end('Content here');
    }).listen(3000);

Associated file extensions

.123, .wks, .wk1, .wk2

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.