I attended the CS50 Spring course, and still use the CS50 IDE. However, as of late my webserver is no longer working! I'm getting the following message in Chrome:

This site can’t be reached

The webpage at https://ide50-bart-koolhaas.c9users.io:8080/ might be temporarily down or it may have moved permanently to a new web address. ERR_TUNNEL_CONNECTION_FAILED

Any idea what might be causing this? Flask is running normally....

Rgds, Bart

  • So you clicked on the CS50 IDE in the upper left and chose "Web Server", or clicked the link flask presents on starting up? My link looks a bit differently, but I do CS50x, and have been registered for a while.
    – Blauelf
    Sep 28, 2017 at 18:07
  • I tried both..... Sep 29, 2017 at 7:06
  • I assume c9users and cs50 in the server name are not to be used interchangably?
    – Blauelf
    Sep 29, 2017 at 11:30
  • Just a guess... is this really old question relevant? cs50.stackexchange.com/questions/16069/…
    – Blauelf
    Sep 29, 2017 at 11:32

2 Answers 2


Sorry guys, it seemed to be caused by the system settings in my office! It works fine from my private laptop.


try this url https://ide50-username.legacy.cs50.io/ dont use the port 8080 it is not working just use the default username url.

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