Behind the scenes

copies index.html as 200.html
starts local web server with your application (by default uses /build as a root)
visits / or any other pages listed in include configuration
find all links on the page with the same domain, add them to queue
If there is more than one page in the queue it also adds /404.html to the queue
renders the page with the help of puppeteer
waits till there are no active network requests for more than 0.5 second
removes webpack chunks, if needed
removes styles with blob URLs, if needed
recreates text for style tags for CSS-in-JS solutions, if needed
inlines critical CSS, if configured
collects assets for http2 push manifest, if configured
minifies HTML and saves it to the disk
if route ends with .html it will be used as is, otherwise route/index.html is used

Other features

react-snap works concurrently, by default it uses 4 tabs in the browser. Can be configured with concurrency option.