Comparators

The seven ways an alert rule can test a metric. For how comparators fit into rule authoring, see Alert rules.

Source of truth: packages/domain/src/alerting/RuleShape.ts (comparatorSpec) and RulePhrase.ts (COMPARATOR_VERB).

Comparator	Reads as	Required fields	Valid metric kinds
`lt`	falls below	threshold	gauge
`gt`	rises above	threshold	gauge
`outside_band`	moves outside	low + high threshold	gauge
`rate`	changes faster than	threshold + window	gauge
`pct_over_baseline`	exceeds baseline by	threshold + baseline + window	gauge
`min_over_window`	stays above	threshold + window	gauge — flow metrics only
`stale`	reports no data for	window	any kind

Notes

Field names. threshold is the trip value; low + high threshold is a band (outside_band); baseline is the reference the metric is measured against; window is a duration in seconds.
min_over_window is the continuous-flow / customer-side-leak detector — a window whose minimum never drops. It is valid only for the flow metric (flow_rate_lpm).
stale is the odd one out: it tests age-since-last-seen, not a value, so it binds to a metric of any kind and only needs a window. Its alert always surfaces as offline.
Every non-stale comparator additionally accepts an optional clear value (hysteresis) and a debounce count — see Alert rules.