You can use mat1's pinger!

You can find it here

Hopefully this answers your question :)

You can either get the hacker plan OR you can set up a server using Sun's httpserver library then ping that using UptimeRobot.

https://replit.com/@SixBeeps/JavaHTTPServer#Main.java

You need to buy the hacker plan, it's on sale right now: https://replit.com/pricing