Downtime
Downtime is the period during which a website, server, or online service is unreachable or not working correctly — the direct opposite of uptime. If a site is down, visitors cannot reach it, transactions fail, and the business behind it gets no benefit from the site's existence for as long as the outage lasts.
Common causes of downtime
Downtime has many possible causes, and they are rarely the same twice: server hardware or software problems, server overload under traffic spikes, an application error introduced by a recent deploy, network or routing problems between the server and the wider internet, DNS misconfiguration, an expired SSL certificate, or a mistake made during maintenance. The first step in fixing any of them is detecting the failure — you cannot fix what you do not know is broken. Website monitoring services check a site from the outside on a regular schedule and alert you the moment something fails, giving you a head start over waiting for a customer complaint. Once an alert fires, server logs are usually the fastest way to find the underlying cause; if you don't have direct access to them, your hosting provider can generally pull them for you.
How downtime is measured
Downtime is normally tracked as a duration (minutes, hours, or days) within a period, and as the flip side of an uptime percentage: 99.9% uptime over a year corresponds to about 8 hours 45 minutes of downtime; 99% uptime corresponds to roughly 3 days 15 hours. See the uptime entry for the full percentage-to-downtime breakdown. What counts as "acceptable" downtime depends heavily on the service — a few minutes of downtime for a personal blog is a non-event, while the same few minutes on a checkout page during a sale can mean real lost revenue.
Detecting downtime before your customers do
External monitoring is what turns downtime from a customer complaint into a controlled incident. Checks run at a fixed interval from multiple locations, so a real outage is confirmed — not just a single flaky connection from one region — before you're alerted by email, SMS, voice call, or messenger. The faster the detection, the shorter the effective downtime, since the clock on an outage keeps running until someone notices and starts fixing it.
How HostTracker detects downtime
HostTracker checks sites from 300+ locations worldwide across 14 check types, including HTTP/S, ping, TCP port, transaction, and content checks, so an outage is caught however it manifests — a dead server, a broken page, or a service that responds but returns the wrong content. Run a free check right now with the website down checker, or set up continuous distributed monitoring so you're alerted automatically the next time something breaks. For more on why this matters, see why websites need monitoring.