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

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

application/x-br signals that a file is compressed using the Brotli algorithm.
It lets software know that the file needs Brotli decompression before use.
This compression is popular in modern web servers and browsers to speed up page loads and reduce data size.

Key uses include:

Web Content Delivery: Optimizes website performance by compressing HTML, CSS, and JavaScript files.
Data Transfer Efficiency: Reduces bandwidth use when serving files over networks.
Resource Storage: Helps in archiving and storing files in a smaller size.

Files compressed this way usually have the BR extension.
For more details on Brotli, visit Brotli compression.

Associated file extensions

.br

Usage Examples

HTTP Header

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


    Content-Type: application/x-br

HTML

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


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

Associated file extensions

.br

FAQs

What is an application/x-br file?

An application/x-br file is a data file compressed using the Brotli algorithm. This compression method is widely used on the web to shrink text-based assets like HTML, CSS, and JavaScript, allowing them to load significantly faster in browsers.

How do I open a .br file on Windows or macOS?

You cannot view a .br file directly because it is a compressed archive. To access the original content, you must decompress it using command-line tools like the Google Brotli utility or file archivers that support the format, such as 7-Zip (often requiring a specific plugin).

Why is my browser downloading a .br file instead of displaying the webpage?

This usually happens due to a server misconfiguration. If a web server sends a compressed file with the application/x-br MIME type but fails to include the correct Content-Encoding: br HTTP header, the browser treats it as a downloadable binary file rather than decoding and displaying the content.

How does application/x-br compare to Gzip?

Files compressed with Brotli (application/x-br) typically achieve a higher compression ratio than those using standard Gzip (application/gzip). This results in smaller file sizes and faster transfer speeds, making Brotli the preferred choice for modern static web assets.

How do I configure Nginx to serve pre-compressed Brotli files?

To serve static .br files, you must enable the ngx_http_brotli_static_module and set brotli_static on; in your Nginx configuration. This tells the server to look for a pre-compressed file with the .br extension alongside the requested resource.

Is application/x-br supported by all browsers?

While almost all modern browsers (Chrome, Firefox, Edge, Safari) support Brotli decompression via HTTP headers, they do not natively support opening standalone .br files from the local file system. The support is designed for web traffic optimization.

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.