Browsers Are Not Refreshing
1. Try another preview address
Open the Server Popover in CodeKit by clicking the button in the top right. There are three Preview addresses listed. If the Bonjour one is not working, try the Non-Bonjour one.
2. Check your output paths
Browser refreshing may be working fine, you just don't see any changes because your file is not compiling to the spot you think it is. Make sure your Sass file is creating the CSS file that your page includes, for example.
3. Be sure the browser is visible
To save power, macOS won't redraw content in a browser if its window is not visible.
4. Turn off Internet Sharing
Open System Preferences > Sharing and disable Internet Sharing. This service blocks the Bonjour name resolution that makes CodeKit's server work.
5. Disable browser plugins
Some plugins, such as Adobe Edge Inspect, are not compatible with CodeKit. Disable all plugins or try a browser without them installed to verify that they aren't the issue.
Temporarily disable scripts on your page to see if one is conflicting with CodeKit. (Prefix-Free is a known example. Use AutoPrefixer in CodeKit instead.)
7. Verify the content-type
CodeKit will only refresh pages that use the text/html content-type. Inspect your HTTP response headers in the browser's console. If you're viewing a document with text/plain or another content-type, CodeKit can't refresh that.
8. Make sure your LAN is not using "Client Isolation"
For security, some networks (such as public WiFi) enable "Client Isolation", which prevents one device on the network from talking to another. Unfortunately, this means that CodeKit cannot refresh separate devices on that network. Browsers on your Mac will still refresh, however.
9. Be sure the text encoding is UTF-8
If your page uses an encoding other than UTF-8, CodeKit may not parse the contents correctly. It's 2017; there's no reason to use anything but UTF-8 at this point.
10. Be sure your OS is supported
On Apple devices, you must be on iOS 6+. On Android, you must be on 4.3+. On Windows, you must be on IE 10+. Older browsers do not support HTML5 websockets, which is how CodeKit communicates with the page.