2. The Audit Criteria

We exported the top 1,000 UK domains from the Majestic Million and to audit at scale we used the Lighthouse Audit Tool. Using Lighthouse we selected 5 of the 11 total (non-manual) Progressive Web App checks to compare across the sites in the data set. We chose the 5 criteria selected to be a good mix of general good mobile experience and Progressive Web App-specific experiences. You can find out more about the tools and data in section 4 of this research; however the 5 criteria we chose are part of the Baseline Progressive Web App Checklist.


Web app features analysed in this study:

1.   HTTPS – Is the site served over HTTPS?

HTTPS is recommended for your website independent of Progressive Web App features. Using secure protocol provides additional security for personal data, such as credit card information. In addition many newer web technologies such as new browser features, Progressive Web App features and HTTP2 are designed for or in some cases require HTTPS to work. Please note, that in the case of a site using both HTTP and HTTPS URLs without any redirection to the HTTPS version, for example Argos at time of writing; we used the URL referenced in the Majestic Million.  Again with regards to Argos as an example this was the HTTP version at time of audit on November 10th and again when checked on 30th November 2017. As this study is focused on mobile user experience if the URL in the data-set did not redirect when typed into the browser (using Chrome 62) we audited the original URL. Where user redirection took place we audited the destination URL.


2.  Service Worker – Does the site register a Service Worker?

Technically a service worker is a ‘man-in-the-middle’ which can intercept network requests and modify responses; thus managing push notifications, background sync and the delivery of some content whilst out of range of a mobile internet connection. Particularly powerful when a user adds a site to home screen this feature can push content and contribute to a sense of ‘always-on’.


3.  Speed – Is the site interactive in less than 10 seconds on a 3G connection? (<10 Seconds TTFI)

As we have mentioned earlier, many mobile device users are still connecting to the internet via 3G connections which can contribute to slow and frustrating experiences. Whilst it might be useful to improve first meaningful paint, if a site is unusable it is still no good to the visitor. Instead, we are looking for a faster experience from leading sites; therefore the measurement standard is a level of interactivity. On occasion we have abbreviated this to TTFI (time to first interactive).


4.  Add to Home Screen – Does the site prompt the user to ‘‘Add to Home Screen’’?

Along with the service worker script and the features it facilitates, the ability to ‘‘Add to Home Screen’’, which is managed in the App Manifest, is the second main feature of a Progressive Web App that is specific to the app like characteristics.


5.  Content Sized for Mobile Viewport – Do they serve content that fits right to the device viewport, either by serving responsively or adaptively?

One size does not fit all when it comes to mobile internet use. This criteria, along with HTTPS and Time to Interactivity are good practise criteria that work for mobile friendly internet use independent of the Progressive Web App features.


Source: Progressive Web App Checklist

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