---
title: Synthetic vs Real User Monitoring (RUM): what's the difference?
description: Synthetic monitoring and RUM answer two different questions about your site. Here's what each one does, where each shines, and why the best setups use both.
canonical: https://watchfor.io/blog/synthetic-vs-real-user-monitoring
---

# Synthetic vs Real User Monitoring (RUM): what's the difference?

2026-06-06 · WatchFor Team · Monitoring · monitoring, performance, basics

Synthetic monitoring and RUM answer two different questions about your site. Here's what each one does, where each shines, and why the best setups use both.

Your dashboard is a wall of reassuring green. Every check is passing. And yet the support tickets keep coming: *"the site is so slow."* Someone's wrong — but who?

Often, nobody is. Your monitoring is telling the truth about *one* thing while missing *another*. This is the gap between **synthetic monitoring** and **real user monitoring (RUM)** — two approaches that answer different questions. Understanding the difference is how you stop being surprised by your own users.

## Two different questions

- **Synthetic monitoring** asks: *"Is it working right now, when I test it?"* It actively sends scripted requests on a schedule, from controlled locations — whether or not any real person is visiting.
- **Real User Monitoring (RUM)** asks: *"How is it actually performing for the people using it?"* It collects data from real visitors' browsers — their devices, their networks, their experience.

One is a lab test. The other is the real world. Both are useful; they're just useful for *different* things.

## Side by side

| | Synthetic | Real User Monitoring (RUM) |
| --- | --- | --- |
| **How it works** | Scripted checks on a schedule | Data from real visitors' sessions |
| **Runs when** | Always — even with zero traffic | Only when people are visiting |
| **Great for** | Uptime, alerting, catching outages fast | Real-world performance, real devices |
| **Catches** | "Is it down?", slow responses, broken flows | The slow phone on bad Wi-Fi you'd never test |
| **Before launch?** | Yes — test pages before they're live | No — needs real traffic |
| **Consistency** | High (same test every time) | Variable (real-world noise) |
| **Alerting** | Excellent — predictable, on demand | Trickier — depends on traffic |

## Where synthetic shines

Synthetic is the backbone of **uptime monitoring and alerting**:

- It works **24/7**, including at 3am when no one's on the site — so you find out about an outage before your first morning customer does.
- It's **consistent**: the same check every minute means a change in results is a real signal, not noise.
- It can test **before** anything is live — a new page, a staging environment, a critical checkout flow.
- It's perfect for **alerting**, because you control exactly what's checked and how often.

This is why "is my site up?" is almost always a synthetic question.

## Where RUM shines

RUM captures what you can never fully reproduce in a lab: **reality**.

- The customer on a three-year-old phone, on hotel Wi-Fi, halfway around the world.
- The slow third-party script that only misbehaves for *some* users.
- Your true [Core Web Vitals](/blog/core-web-vitals-explained) "field" data — the numbers Google actually uses for ranking.

RUM answers "how does it *feel* for real people?" — a question synthetic checks can only approximate.

## Why you want both

These aren't competitors; they're two halves of the picture:

> **Synthetic tells you when it's broken. RUM tells you when it's merely *bad*.** A site can be 100% "up" on every synthetic check and still feel sluggish to half your users. Without RUM you'd never know; without synthetic you'd find out about outages too late.

The practical split most teams land on:

| Use synthetic for… | Use RUM for… |
| --- | --- |
| Uptime and outage alerting | Real-world performance trends |
| Testing critical flows on a schedule | Understanding your actual user base |
| Pre-launch and staging checks | Field Core Web Vitals (for SEO) |
| Certificate, DNS, API checks | Spotting issues that hit only some users |

## Where WatchFor fits

WatchFor is built on **synthetic monitoring** — scheduled checks from multiple global locations — which is exactly what you want for fast, reliable [uptime alerting](/docs/monitors). It also runs **real-browser** checks for [Core Web Vitals](/docs/monitors/performance), loading your pages the way an actual browser would, so you get performance signals that go beyond a simple "is it up?".

Pair that with RUM from your analytics for field data, and you've got both halves: the early-warning system *and* the real-world view.

## The bottom line

| | In one line |
| --- | --- |
| **Synthetic** | A scheduled lab test — best for uptime and alerting. |
| **RUM** | Real visitors' experience — best for real-world performance. |
| **Together** | Synthetic catches outages; RUM catches "it's just slow". |

If you only have one today, start with **synthetic** — you can't alert on traffic you don't have, and knowing the instant something breaks is the foundation everything else builds on. Then layer RUM on top to see your site through your users' eyes.

New to all this? Start with [Uptime Monitoring 101](/blog/uptime-monitoring-101), or jump into the [monitors guide](/docs/monitors).

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Canonical page: https://watchfor.io/blog/synthetic-vs-real-user-monitoring · All articles: https://watchfor.io/blog/all.md · Site guide: https://watchfor.io/llms.txt