Mailing address:SIA Monkey See Monkey Do
healthchecks.io is an open source project. The code is on GitHub, it has BSD license, and is accepting contributions.
The service is currently run on Hetzner bare metal servers. The app servers are load balanced. The PostgreSQL database has a hot standby as well as full daily backups to S3. The database failover process is manual, and the ops team consists of a single person, so multi-hour or even multi-day outages are possible!
While we can only guarantee a best effort availability, in practice the availability has exceeded 99.9% since the service publicly launched in July 2015. That is, until 20 August 2016, when the service experienced a 24 hour outage.
There's also a number of alternative cron monitoring services, with different feature sets, different reliability guarantees and pricing options. If healthchecks.io doesn't seem like a good fit for you, why not check them out: Cronitor.io, Dead Man's Snitch, Coal Mine, PushMon, steward.io, CronAlarm, Watchdog Timer.