Downlink Header

Table of Content

The Downlink header is a feature in web transfers that provides information about the downstream speed or bandwidth in megabits per second (Mbps), which is available to the user agent or client instance. This attribute is useful for providing adaptive content delivery based on the network conditions currently experienced by a client.


Downlink: <number>

The syntax simply involves the inclusion of the "Downlink" keyword followed by a colon and the bandwidth number in Mbps format.


The Downlink header field has no specific directives. Its function is simply to relay the calculated downstream speed available to the user agent.


Here are some examples of how to utilize the Downlink header:

  • A downlink value of 1.5 in the header Downlink: 1.5 represents a downstream speed of 1.5 Mbps.

  • If the downlink speed is not known, the header returns an empty value like Downlink: .

Browser Compatibility

Browser Compatibility
Chrome Supported
Firefox Not Supported
Safari Not Supported
Opera Supported
Edge Supported

ModHeader is a browser extension that allows users to modify HTTP request headers. Here's an example of how to use ModHeader to modify the Downlink header:

  1. Download and install the ModHeader extension from the Chrome Web Store.
  2. Open the ModHeader extension (it's located near the address bar).
  3. Click on the '+' button to add a new header.
  4. Type "Downlink" in the 'Name' field and enter your desired downlink speed value in the 'Value' field, e.g., '1.5' for 1.5 Mbps.
  5. The updated Downlink header will now be included in all outgoing HTTP requests.

This is particularly useful for web developers, as they can simulate different client-side network conditions and optimize their applications accordingly.