The CodePen Projects editor uses three domains to process your code and display the Project preview.

If one of these domains is blocked or restricted on your network, the Project editor may display a blank page, or your files may show a “Loading File” message.

The domains are:


If you are behind a workplace firewall, you may need to ask your IT team to allow those 3 domains. If you use content-blocking browser extensions, you can adjust the extension’s settings to allow the domains.

Still stuck? Write in to support and we can help!

Was this article helpful?