PeoplesGeek

Monitoring services like www.siteuptime.com or www.montastic.com require a page on your website to monitor.
This plugin provides a virtual target for your monitoring services that does not invoke other plugins (specifically avoiding the Google analytics plugins so that your statistics are not skewed by monitoring calls) 
The two targets provided for the monitoring service are:
<ul>
<li>monitor.htm – via .htaccess and does not use WordPress (but does use PHP)</li>
<li>monitorWP.htm – via WP and so tests the Database etc is working</li>
</ul>

PG Monitor

A virtual target file to be read by monitoring services instead of using a static HTML page.

santerref

This plugin simplifies how you can add for you by giving you a configuration page to put the code.
Once installed, a new REST API route will be created to output the code: wp-json/mywebsiteisonline/v1/verify
Trusted by developers from all around the world.
<h4>My Website is Online features</h4>
Receive a notification as soon as a problem is detected on your website.
<ul>
<li>1-minute checks</li>
<li>Unlimited monitors</li>
<li>SMS alerts</li>
<li>Unlimited email alerts</li>
<li>HTTP headers and status</li>
<li>Response time monitoring (TTFB)</li>
<li>SSL certificate checks</li>
<li>Multi-factor authentication</li>
<li>12 months log retention</li>
<li>Multiple email recipients</li>
<li>Domain expiration monitoring</li>
<li>Google Web Risk</li>
<li>DNS records monitoring</li>
<li>Slack integration</li>
</ul>
To learn more about My Website is Online visit: <a href="https://mywebsiteisonline.com/" rel="nofollow ugc">https://mywebsiteisonline.com/</a>

Uptime Monitoring for WordPress – My Website is Online

Thanks for the plugin, help me linking my website to My Website is Online.

Simple and works perfectly

My Website is Online is a Web service that monitors your website every minute to check if it's down. Don’t let downtimes impact your business.

PG Monitor vs Uptime Monitoring for WordPress – My Website is Online