A service worker should be registered in order to enable the typical features of a PWA.
Why register a service worker?
In order to enable the typical features of a PWA (Progressive Web App), the first thing that should be done is to register a service worker; in this way, the PWA can be installed on the device chosen by the user, can enable push notifications and can function without an Internet connection.
Service Workers are compatible with almost all major browsers (the only one that does not work is Internet Explorer).
How the SeoChecker service worker audit is displayed
If a page has not registered a service worker, SeoChecker will notify it.
How can I register a service worker?
Registering a service worker involves only a few lines of code, but the only reason you'd use a service worker is to make it possible to implement one of the PWA features outlined above. Actually implementing those features requires more work, therefore we'll refer you to Google's guides: