How Alert Rules Work

How Alert Rules Work

An alert rule defines the condition under which PulseAPI creates an incident and sends notifications. This article explains the evaluation flow, the components of a rule, and common configuration patterns.

The Evaluation Flow

After every check, PulseAPI evaluates the check result against all active alert rules. Here's what happens step by step:

  1. Check completes — PulseAPI records the status code, response time, and any errors.
  2. Rule evaluation — Each active alert rule is checked: does this result meet the rule's condition?
  3. Cooldown check — If the condition is met, PulseAPI checks whether the rule's cooldown period has elapsed since it last fired. If it hasn't, the rule is skipped to prevent notification spam.
  4. Incident creation — If the condition is met and the cooldown has cleared, PulseAPI creates an incident.
  5. Notification dispatch — Notifications are sent to all channels assigned to the rule.

Rule Components

Condition Type

The metric the rule measures:

  • Response time — how long the request took in milliseconds
  • Status code — the HTTP status code returned
  • Uptime percentage — uptime over a time window (e.g., last 24 hours)
  • SSL certificate expiry — days until the SSL cert expires

Operator and Threshold

Together, these define the failure condition. For example:

  • Response time greater than 2000 (ms)
  • Status code is not 200
  • Uptime percentage less than 99.9 (%)
  • SSL expiry less than 14 (days)

Scope

Whether the rule applies to all monitors on your team or only specific ones:

  • Team-wide — applies to every monitor
  • Endpoint-specific — applies only to the monitors you select

Notification Channels

Which channels receive a notification when the rule fires. A rule can notify multiple channels. Channels must be created before they can be assigned to a rule.

Cooldown Period

How long PulseAPI waits before firing the same rule again after it last triggered. This prevents a single episode of failures from generating dozens of notifications.

For example, a 30-minute cooldown means: if a rule fires at 2:00 PM, it will not fire again until 2:30 PM even if checks continue to fail.

Priority

Sets the severity of the incidents this rule creates: Critical, High, Medium, or Low. Higher priority rules create higher-severity incidents. See Setting Rule Priority.

Example: A Practical Rule Configuration

Goal: Get a Critical alert if the production API returns anything other than 200.

  • Condition: Status code
  • Operator: is not equal to
  • Threshold: 200
  • Scope: Endpoint-specific — select "Production API"
  • Notification channels: Slack (#incidents), Email (on-call@yourapp.com)
  • Cooldown: 15 minutes
  • Priority: Critical

Multiple Rules

You can have multiple alert rules active simultaneously. They're evaluated independently. A single check result can trigger multiple rules at once (e.g., if a check times out, both a "response time" rule and a "status code" rule could fire).

Tip: Start with broad, team-wide rules to catch everything, then add specific rules for your most critical monitors with tighter thresholds and higher priority.

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