If you are presented with a blank screen or you find the simulator is missing in MakeCode, you may need to configure your firewall to allow specific websites. Here is a list of requirements for each editor and tool.



To enable some additional features for extension developers, the following domains are also needed. In most cases, you won’t need to unblock these domains:

Python Editor

  • microbit.org and subdomains (*.microbit.org)
  • readthedocs.io and subdomains(*.readthedocs.io)
  • readthedocs.org and subdomains(*.readthedocs.org)


as above and including

 *.pusher.com (enable web socket connections if possible)


micro:bit classroom will use WebRTC if possible


If you are using a proxy server within a school environment, you may need to exclude the scratch link URL and port from using the proxy http://device-manager.scratch.mit.edu:20110/ 

This is set on the client and not the firewall or proxy.

How to set up an exclusion depends on how the machine's proxy settings have been configured in the first place.  This is often done through Windows Group Policy, but may instead be done through a WPAD or PAC file or configured manually on each workstation. (Source: Opendium)