Google Lighthouse

 Google Lighthouse  is an open source website testing tool for improving “performance, accessibility, progressive web apps, SEO”, that can be run via a website or in Chrome Dev Tools, and used by several members of the IndieWeb community to improve their personal sites.

It rates each point on a scale of 0-100 based on certain metrics.

Web-based version:
 * Google PageSpeed Insights

Why
Google Lighthouse is a tool for developers to improve their websites, and users can also use it to view a coarse evaluation of websites that they use, to provide feedback and requests to the developers of said websites.

Open Source

 * https://github.com/GoogleChrome/lighthouse

IndieWeb Examples

 * Max Böck: 2017-01-16: The Relaunch Post

Scores not indicative of quality

 * 2019-05-31 Building the most inaccessible site possible with a perfect Lighthouse score