The agent will make the check pass
Given a red signal, an agent optimises for the signal. That is not a flaw in any particular tool — it is what optimisation means, and it changes which signals are worth having.
Reliability
Everything in The Nest tagged Reliability.
Your monitor cannot live in the thing it monitors
A health check inside your own stack goes silent at exactly the moment it had something to say. Here are the failure domains an internal check shares with the site, and what an external one sees instead.
The agent shipped it and nobody read it
An AI agent can produce a working-looking site faster than any human can review it. The defects live in the gap between the agent saying it is done and a stranger being able to use it.
Knowing before your customers do is the whole product
Monitoring is usually justified as insurance against downtime. The better argument is commercial: the gap between a customer telling you your site is broken and you telling them is a gap they can feel.
Why certificates still lapse, twelve years after Let's Encrypt
Renewal is automated almost everywhere and certificates still expire in production. The failure has moved: it is no longer the renewal that breaks, it is everything between the renewal and the socket a browser actually connects to.
Two nulls are not zero
A monitoring dashboard has three ways of not knowing something, and every one of them has been drawn as a confident zero at least once. Here is why that is the most expensive bug a status screen can have.
Thirty-one checks, one grid
HarpyWatch runs thirty-one distinct kinds of check against a site — not thirty-one variations on an HTTP request. Here is the full list, what each one is actually for, and why they share a single screen.