Uptime Robot's observability is very limited, as it only offers Synthetic Monitoring. If you want a true overview of your website, applications, servers, and the rest of your stack, then Uptime Robot alone won't be enough.
Sematext not only offers Synthetic Monitoring, but Log Monitoring, Infrastructure Monitoring, and Real User Monitoring, too. With Sematext, when API checks start failing, you can use Log Monitoring to locate the root cause of the problem. This is something you can't do with Uptime Robot.