Download XLivePreview.zip from this release (under this text) and unzip it.
Move the app into your Applications folder
Run the app so swift icon will be visible near the clock in the top bar
Go to your swifweb project and create empty Package.xpreview file in the root folder near the Package.swift file
Then add new editor in the right (Ctrl+Cmd+T) and open there the Package.xpreview
Then click to your left editor and go to any swift file which contains WebPreview and press Cmd+S there once
On the right side above the swift logo you will see the yellow circle which indicates that live preview is building now, it may take about a minute for the first time since it is compiling the whole project from scratch. Then when it is finished you will see the preview and circle indicator became green.
Later when you made any changes in the file just hit Cmd+S to update livepreview.
When you switch to another file just hit Cmd+S inside it to see its livepreview.
Congrats, now you can code your swifweb app in beolved Xcode with an awesome livepreview right inside of it and be super productive! 🚀
UPD Jan 2022: This app is now works well on both Intel and Apple Silicon macs!