Knowing how the site actually performs.
WHAT TO MEASURE
Server response time, which reflects your application Total page load time, which reflects assets too Error rates Database query counts and durations Resource usage against plan limits
TOOLS
External uptime and speed monitoring, checking from outside on a schedule Application performance monitoring, where budget allows Profiling tools during development cPanel resource usage graphs
WHAT TO ALERT ON
The site being unreachable Response times exceeding a threshold Error rates rising Resource limits being approached
Alert on things requiring action. Alerting on everything trains you to ignore alerts.
ESTABLISHING A BASELINE
Measure normal performance now, so you can recognise degradation later. Without a baseline, "the site feels slow" is unfalsifiable.
WATCHING TRENDS
Gradual degradation over months is the common pattern, usually from data growth outpacing indexes. Trends reveal it; spot checks do not.
REAL USER DATA
Analytics reporting actual load times from visitors tells you more than synthetic tests from one location.