Shawn Hooper

This plugin generates a list of all the custom page templates available in the active WordPress theme, and shows you how many pages use this template. 
It will also show you if the page contains any Gutenberg blocks or not.
You can also click on the count to access the list of pages that use a specific template.

Page Template Usage Info

Shows you which pages are using which templates, and whether or they are built with Gutenberg or not.

Weston Ruter

Felix Arntz

Google

As <a href="https://developers.google.com/web/updates/2018/09/reportingapi" rel="nofollow ugc">noted on the Google Developers blog</a>:
<blockquote>
The Reporting API defines a new HTTP header, <code>Report-To</code>, that gives web developers a way to specify server endpoints for the browser to send warnings and errors to. Browser-generated warnings like CSP violations, Feature Policy violations, deprecations, browser interventions, and network errors are some of the things that can be collected using the Reporting API.
</blockquote>
This plugin provides a storage mechanism and endpoint for browser reports according to the Reporting API spec in WordPress, as well as an admin interface for browsing these reports. It also provides an API for sending the <code>Report-To</code> response headers.
As the Reporting API specification is still evolving and at an early stage, the plugin reflects that and is currently an experimental prototype, to demonstrate how Reporting API can be used in WordPress.
<h4>Did you know?</h4>
There is also a new specification called Feature Policy which will integrate with the Reporting API specification. There is a <a href="https://wordpress.org/plugins/feature-policy/" rel="ugc">WordPress plugin for Feature Policy</a> as well.

Reporting API

WordPress plugin for receiving browser reports via a Reporting API endpoint.

Page Template Usage Info vs Reporting API