Observability45-75 min
Real User Monitoring with Web Vitals
Instrument LCP, CLS, INP, and navigation metadata so production performance regressions become visible.
web-vitalsSentryDatadogAnalytics
Prerequisites
- A production frontend app.
- An analytics or logging endpoint.
- A privacy policy for telemetry collection.
1
Plan the implementation
Start by choosing the exact page, route, API, or deployment surface you want to improve. A narrow target makes the implementation measurable and easier to verify.
- Write down the current behavior and the user-facing problem it creates.
- Pick one measurable success signal such as bundle size, latency, error rate, security coverage, or UI responsiveness.
- Identify the files, routes, providers, and environment variables involved.
- Create a rollback note before changing production-sensitive configuration.
2
Set up the required tools
Install or configure only the tools needed for this implementation. Keep config close to the feature so future developers can find the moving parts quickly.
Implementation snippet
npm install web-vitalsChecklist
- Dependencies are added to the correct workspace package.
- Environment variables are documented in `.env.example` when needed.
- Local development still starts without production-only secrets.
- The change is small enough to review in one pull request.
3
Implement the core pattern
- Install the Web Vitals client library.
- Create a lightweight endpoint that accepts metric payloads.
- Include route, device class, connection type, and app version when safe.
- Sample traffic if volume is high.
- Create a dashboard grouped by route and metric percentile.
Implementation snippet
import { onCLS, onINP, onLCP } from "web-vitals";
function send(metric) {
navigator.sendBeacon("/api/metrics/web-vitals", JSON.stringify(metric));
}
onCLS(send);
onINP(send);
onLCP(send);4
Handle edge cases
Checklist
- Metrics are collected only in production or controlled preview environments.
- Payloads avoid private user data.
- P75 values are tracked for key routes.
- Alerts trigger on regressions, not normal metric noise.
5
Verify before production
- Run the app locally and test the normal success path.
- Test one failure path, one empty state, and one slow-network or retry path.
- Run the project build and any related unit or integration tests.
- Check browser console, server logs, and network responses for hidden warnings.
- Document the final behavior, commands used, and any follow-up work.