A few months ago a team I know shipped a routine Friday deploy. Every monitor stayed green all weekend. On Monday they discovered the signup form had been throwing a JavaScript error since Friday afternoon. The server was returning 200 OK the whole time. The page loaded. The HTML was valid. And not a single person could create an account for three days.
Nobody filed a bug. Customers don't file bugs. They hit a wall and leave.
This is the uncomfortable truth about most monitoring setups: they answer "is the server responding?" when the question that actually matters is "can a customer do the thing they came to do?" Those are not the same question, and the gap between them is where revenue quietly leaks out.
Why 200 OK lies
A classic uptime check does roughly this:
