What is MIME type "application/atomcat+xml"?

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

The MIME type application/atomcat+xml defines an XML document used to list and organize categories for Atom feeds. This type is part of the Atom Publishing Protocol family, which standardizes how clients discover allowed categories on a server.
It lets client applications query a server for a set of category terms applicable to content submissions.

Key uses include:

Content categorization – Enables grouping of entries for better organization.
Service discovery – Allows clients to find which categories are supported.
Interoperability – Ensures that Atom-based systems handle category data consistently.

Files using this MIME type may appear with the extension ATOMCAT.
For more details on the protocol, refer to the Atom Publishing Protocol (RFC 5023).

Associated file extensions

.atomcat

Usage Examples

HTTP Header

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


    Content-Type: application/atomcat+xml

HTML

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


    <a href="file.dat" type="application/atomcat+xml">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/atomcat+xml');    
      res.end('Content here');    
    }).listen(3000);

Associated file extensions

.atomcat

FAQs

What is the primary use of the application/atomcat+xml MIME type?

This MIME type identifies an Atom Category Document, which is defined in the Atom Publishing Protocol (RFC 5023). It is used to provide a machine-readable list of categories that can be applied to entries in an Atom feed, helping clients validate tags before submission.

Which file extension is associated with application/atomcat+xml?

The standard file extension for this MIME type is .atomcat. You can find more details about this extension on our atomcat page.

How does application/atomcat+xml differ from application/atom+xml?

While application/atom+xml represents the actual Atom feed or entry content, application/atomcat+xml is a helper format used specifically for metadata. It lists the categories (tags) allowed by the server, whereas the former contains the actual articles or data.

How do I configure Apache to serve .atomcat files correctly?

To ensure your Apache server sends the correct headers, add the following line to your .htaccess file or httpd.conf: AddType application/atomcat+xml .atomcat. This prevents clients from misinterpreting the file as generic text or XML.

Why does my web browser display raw code when I open an .atomcat file?

Most web browsers do not have built-in rendering logic for Atom Category Documents. Since the format is XML-based, browsers usually display the raw XML tree or prompt you to download the file. This is expected behavior as the format is intended for software clients, not direct human reading.

Is application/atomcat+xml required for a standard RSS/Atom reader?

No, standard feed readers (aggregators) typically do not use this file type. It is primarily used by publishing software (like blog editors) to discover which categories exist on a server so the user can select them when writing a new post.

How do I add support for this MIME type in Nginx?

In your Nginx configuration file (often nginx.conf or inside sites-available), add the mapping inside the types block: types { application/atomcat+xml atomcat; }. Reload Nginx to apply the changes.

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.