How to specify a base url or host port for Jetbrains Rider asp.net project

This can be done inside the Rider IDE if you like.

If you edit the run/build configuration you are using when you hit F5 and then edit the environment variables you can add the ASPNETCORE_URLS environment variable which will run the app using the port specified as shown here.

Rider Run configuration environment variables

Steps to edit the setting

1. Open the edit screen for the run/build configuration
2. Click the ellipsis on the environment variables edit box to edit
3. Click the plus (+) symbol to add a new evironment variable
4. Set the name to ASPNETCORE_URLS and the value to http://*:57243
5. Save your changes and run

It turned out that the option in Visual Studio just changes the application.config in the .vs folder. A similar file in the .idea folder had the properties of the ports.

Changing it in that file fixed it.

@Sasquatch's answer works for ASP.NET Core only.

For plain old ASP.NET, with IIS Express, we can go the project properties, Web section, and then

• Make sure "Server type:" is "IIS Express".
• Check "Generate applicationhost.config". [*]
• Set "URL:" to "localhost".
• Set "Development port:" to whichever port you want ("1234" in this example).
• Click "OK" and restart the web application.

This will rewrite the generated applicationhost.config file (in .idea\config\ folder) with your selected configuration.

[*] If "Generate applicationhost.config" is unchecked, you should edit that file directly, like @WWietlol's answer suggests.