Sometimes, lessons and labs include directions to start a local development server that can be accessed at localhost  in your web browser. For labs that use Rack, that usually means localhost:9292 ; for Shotgun, localhost:9393; and for Rails, localhost:3000.

localhost is a network address that points to your own computer. Navigating to localhost:3000 in your web browser sends a request to the Rails development server running locally on port 3000. However, this only works if your web browser is running on the same computer as the development server.

When you execute code in the IDE terminal, the code is run on a Learn IDE server in the cloudnot on your computer. Because of this, firing up a development server in the IDE will not make pages accessible via localhost:3000  on your local machine. Instead, pay attention to the output from the rackup , shotgun , or rails s  command; it will always tell you which address to navigate to in your local browser:




To view HTML pages in the browser without starting a Rack, Shotgun, or Rails server, check out this Help Center article.

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