You can get free uptime monitoring from Google Cloud. The limit is 100 uptime checks per monitoring scope, which may mean either a project or an organization based on how you configure IIUC. https://cloud.google.com/monitoring/uptime-checks. The checks are ran from 6 locations around the world, so you can also catch network issues, that you likely cannot do much about when you're running a tiny service. My uptime checks show the probes come from: usa-{virginia,oregon,iowa}, eur-belgium, apac-singapore, sa-brazil-sao_paulo

Another neat monitoring thing I rely on is https://healthchecks.io. Anything that needs to run periodically checks in with the API at the start and the end of execution so you can be sure they are running as they should, on time, and without errors. Its free tier allows 20 checks.

It works really well for cron jobs - while it works with a single call, you can also call a /start and finished endpoint and get extra insights such as runtime for your jobs.

It would be nice if it had slightly more complex alerting rules available - for example, a "this service should run successfully at least once every X hours, but is fine to fail multiple times otherwise" type alert.

We wanted to use it for monitoring some periodic downloads (like downloading partners' reports), and the expectation is the call will often time out or fail or have no data to download, which is technically a "failure", but only if it goes on for more than a day. Since healtchecks.io doesn't really support this, we ended up writing our own "stale data" monitoring logic and alerting inside the downloader, and just use healtchecks.io to monitor the script not crashing.