Glossary · Monitoring

Baseline (Monitoring)

A monitoring baseline is the normal range of a metric over time, such as typical response time or traffic, used to judge whether current values are abnormal.

Updated October 6, 2026

A baseline is a record of how a system normally behaves. It is built from historical data for metrics like response time, error rate, CPU use or requests per minute, often split by hour of day and day of week.

Why it matters

Raw numbers mean little without context. A response time of 900 ms might be fine for a heavy report and a disaster for a login endpoint. Baselines let you set thresholds from evidence instead of guesses and make it easier to spot slow drift, such as latency creeping up after each release. They also feed anomaly detection.

Example

A shop's homepage response time from a month of checks:

weekday daytime: median 420 ms, p95 780 ms
night:           median 380 ms, p95 600 ms

A reasonable warning might be p95 above 1,200 ms for five minutes, which is clearly beyond normal variation without being triggered by it.

Common mistakes

  • Building a baseline during an unhealthy period, then treating bad as normal.
  • Ignoring seasonality such as sales events, month-end or school terms.
  • Never refreshing it after major architecture changes.
  • Using a single global figure for traffic that has strong daily cycles.

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