Progressive Web Apps (PWAs) must work offline. To determine whether a page is accessible while the user is offline, Lighthouse checks that the page sends an HTTP 200 response, which indicates that the request for the page was successful.
Learn more in the What is network reliability and how do you measure it? post.
How the Lighthouse offline audit fails
Lighthouse flags pages that don't respond with a 200 when offline:
Each PWA audit is weighted equally in the Lighthouse PWA Score, except for three manual audits: Site works cross-browser, Page transitions don't feel like they block on the network, and Each page has a URL. Learn more in the Lighthouse Scoring Guide.
How to make your PWA work offline
- Add a service worker to your app.
- Use the service worker to cache files locally.
- When offline, use the service worker as a network proxy to return the locally cached version of the file.
Try it! Learn how to add a service worker to your app with the Working with service workers codelab.
- Source code for Current page does not respond with a 200 when offline audit
- What is network reliability and how do you measure it?
- Service Workers: an Introduction