A monitoring dashboard that collects LCP data but has no alert threshold for regression is a passive tool — it shows you that LCP increased from 1.8s to 3.2s only after someone manually checks the dashboard. ISO 25010:2011 time-behaviour requires measuring and acting on performance data; an alert on LCP regression > 200ms converts monitoring from a reporting artifact into an active safety net. Without alerts, performance regressions persist in production for days or weeks before anyone investigates.
Info because alerts are a meta-control on existing monitoring — their absence does not cause performance failures directly, but reduces the team's mean time to detect regressions from minutes to days.
Define alert thresholds in your monitoring service (Datadog, New Relic, Sentry, or Grafana) for each Core Web Vital. For code-defined thresholds, document them in a constants file and reference them in your alert configuration.
// lib/monitoring/thresholds.ts
export const PERFORMANCE_THRESHOLDS = {
LCP_MS: 2500, // alert if LCP regresses above this
CLS: 0.1, // alert if CLS exceeds this
INP_MS: 200, // alert if INP exceeds this
LCP_DELTA_MS: 200, // alert if LCP worsens by more than this vs. 7-day baseline
}
ID: performance-deep-dive.regression-prevention.regression-alerts-configured
Severity: info
What to look for: Count all alert configurations. Enumerate thresholds for LCP (no more than 2.5s), CLS (no more than 0.1), and INP (no more than 200ms). Check monitoring dashboard for alert rules. Look for thresholds on LCP, CLS, FID/INP regressions. Verify alerting is configured (Slack, email, PagerDuty).
Pass criteria: Alerts configured for LCP regression (>100ms), CLS regression (>0.02), FID/INP regression. Alerts are sent to team channels (Slack, email).
Fail criteria: No alerts configured, or alert thresholds are too loose.
Skip (N/A) when: Never — alerts prevent performance regressions from going unnoticed.
Cross-reference: For threshold review schedule, see alert-thresholds-reviewed.
Detail on fail: "No alerts configured — LCP increased from 1.8s to 3.2s undetected for 2 weeks" or "Alert threshold too loose: only alerts if LCP > 5s (users suffer well before that)"
Remediation: Configure monitoring alerts in your service's dashboard with thresholds for LCP, CLS, and FID/INP regressions.
// lib/monitoring/alerts.ts — alert thresholds
const ALERT_THRESHOLDS = { LCP: 2500, CLS: 0.1, INP: 200 }