If you're using the Google App Engine Launcher, you can't stop the web server once it's started. However, there are a few ways to work around this:
-If you just need to stop the server for a short period of time, you can go to the "Edit" menu and select "Preferences". In the "Server" tab, you can select how long the server should run before it shuts down automatically.
-If you need to stop the server for a longer period of time, you can go to the "File" menu and select "Exit". This will close the Launcher, and the web server will no longer be running.
-If you need to stop the server permanently, you can go to the "File" menu and select "Remove Application". This will remove the application from the Launcher, and the web server will no longer be running.