---
title: "Real User Monitoring (RUM) — monitoring glossary"
description: "Real User Monitoring (RUM) captures actual page load performance in real visitors' browsers — LCP, INP, CLS, TTFB — instead of synthetic tests. RUM answers…"
canonical: "https://lemwatch.com/glossary/rum"
source: "https://lemwatch.com"
---

# Real User Monitoring (RUM)

> Real User Monitoring (RUM) captures actual page load performance in real visitors' browsers — LCP, INP, CLS, TTFB — instead of synthetic tests. RUM answers 'what do users actually experience?' while synthetic monitoring answers 'is the site up and…

**Also known as:** Real-User Monitoring, End-User Experience Monitoring

## Definition

 RUM works by injecting a small JavaScript beacon that reports Web Vitals back to a collector when the page finishes loading. Because it samples every real session, it reveals problems synthetic checks miss: slow devices, poor networks, geographic tail latency, edge-case browser bugs.

 RUM is the source of truth for Core Web Vitals ranking signals — Google uses the CrUX dataset (aggregated Chrome RUM) to decide whether a URL passes the CWV thresholds. Lemwatch pulls CrUX data directly and pairs it with synthetic Lighthouse runs for the full picture.

## Why it matters

 Without RUM, you optimise for the lab and ship regressions to the field. Slow real-user LCP is what Google actually ranks — synthetic PageSpeed scores are a proxy, not the ground truth.

 See it in the product: [Core Web Vitals monitoring](https://lemwatch.com/features/core-web-vitals).


## Related

- [Monitoring glossary](https://lemwatch.com/glossary)
- [Core Web Vitals](https://lemwatch.com/glossary/core-web-vitals)
- [LCP](https://lemwatch.com/glossary/lcp)
- [INP](https://lemwatch.com/glossary/inp)
- [CLS](https://lemwatch.com/glossary/cls)
- [Status Page](https://lemwatch.com/glossary/status-page)
- [All monitoring checks](https://lemwatch.com/features)
- [Schema Markup](https://lemwatch.com/glossary/schema-markup)