Each endpoint has:

• Name (string, human readable, short for preference)
• Uri
• LastChecked (Timestamp)
• LastSuccess (Timestamp)
• FailedCheckCount (number, default 0)
• LastAlert (Timestamp?)
• Enabled (bool, default true)

Timestamps are probably going to be ISO format, but they could just be counts (although storing wallclock time does allow for periodic reminders)

A healthy host has last success equal to last checked.

Each failed check adds one to FailedCheckCount. A successful check resets FailedCheckCount to zero.

If FailedCheckCount is over a specified threshold, then an alert is sent and LastAlert is set.