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GitHub Codespaces port forwarding connection refused

29 Nov 2022 | 5 minute read

GitHub recently announced that Codespaces is available for everyone. If you need to know what Codespaces is, check it out here. Basically, it is Visual Studio Code running on a VM in Azure available from your web browser.

I wanted to play around with Codespaces, so I created a new .NET web API project. As I have always been a Visual Studio user for .NET development, using Codespaces for .NET was a new experience.

.NET webapi project

Let’s first create a new .NET project. To do this, you can run the following command

 dotnet new webapi --language "C#"

This will create a new .NET web API project with essential items like a controller and support for swagger.

You can run this project by executing the following command.

 dotnet run

This will start the project in Codespaces, and you can use a browser on your local machine to access the web API. The idea is that you can use it just like you do on your local development machine.

Port Forwarding Issue

When you run your project, you will see a pop-up in your code spaces telling you you can browse your website on the HTTP port. Codespaces creates port forwarding to your local machine so you can interact with the web API. But if you click the `Open in browser button in the popup, you will not be able to open the site.

The issue here is that the default .NET web API project does port forward to the HTTPS. So you will be redirected to the localhost HTTPS port, which is not supported within Codespaces.

The easiest way to fix it is to remove the following line.


This will stop the default HTTPS forwarding, and you will be able the use the HTTP port again. There might be a better solution than this one. Removing this line is not that secure when running this web API in a production environment.

So, what if we do not want to remove the line? What other options do we have? When you use the dotnet run command to start your project, the terminal will show something like this.

 Now listening on https://localhost:7198.
 Now listening on http://localhost:5000.

You can click on these URLs to open the website, but as we already know, the localhost:5000 does not work. If you click on the HTTPS URL, you will see the website appear.

There is another option to access the HTTP port if you want. On the Ports tab, you can Copy the local address; this will copy the You can use this address in your browser address bar. If you paste it like this, it will still use the forward to HTTPS, and the website will still not appear.

But if you use this address with, for example, /swagger behind the URL, it will show the swagger page. The same goes for the other controllers like the default /WeatherForecast as long as you do not use the root.



I work as a consultant for Xebia. I am passionate about problem-solving for customers with the help of technology. I love to learn new techniques, technologies and ways to improve myself.