Synthetic Monitoring vs Real User Monitoring

Synthetic monitoring and real user monitoring (RUM) are both used to understand how your website or application performs — but they collect data in fundamentally different ways and serve different purposes. Choosing between them (or combining them) depends on what questions you're trying to answer.

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What Is Synthetic Monitoring?

Synthetic monitoring uses scripted bots that simulate user behaviour on a schedule. A synthetic monitor might:

• Navigate to your login page every 5 minutes and check the page loads
• Complete a checkout flow once per hour and verify the confirmation page appears
• Call an API endpoint and validate the response body

Because synthetic monitoring is scripted and scheduled, it's proactive — it runs whether or not real users are on your site. It can detect issues at 3am on a quiet Tuesday before any real users encounter them.

For a full introduction, see what is synthetic monitoring.

Synthetic monitoring strengths:

• Detects issues before users encounter them
• Consistent, repeatable tests — always the same script, same conditions
• Works around the clock regardless of traffic levels
• Provides uptime metrics and SLA evidence
• Tests specific user flows with assertions

Synthetic monitoring limitations:

• Tests a scripted path, not all the varied ways real users interact
• Doesn't capture the diversity of real user devices, browsers, and network conditions
• A synthetic test that passes doesn't guarantee all users have a good experience

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What Is Real User Monitoring?

Real user monitoring collects performance and availability data from actual users as they use your site. A RUM library embedded in your pages captures:

• Page load times and Core Web Vitals
• JavaScript errors
• API call latency as experienced by users
• Geographic distribution of performance data
• Browser and device breakdowns

RUM is passive and reactive — it measures what's actually happening to real users, but only when they're present.

For a full introduction, see what is real user monitoring.

RUM strengths:

• Real-world data from actual user devices and networks
• Catches issues that only affect specific browsers, regions, or connection types
• Reveals performance issues that synthetic tests miss (real network conditions, real device variability)
• Proportional to actual user impact — high-traffic pages generate more data

RUM limitations:

• No data when there are no users (nights, weekends, low-traffic periods)
• Can't proactively test before deploying changes
• Requires JavaScript instrumentation in your pages
• Not useful for early-stage products with low traffic

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The Core Difference

	Synthetic	Real User Monitoring
Data source	Scripted bots	Actual users
Timing	Scheduled, continuous	When users visit
Low-traffic coverage	Yes	Limited
Detects issues proactively	Yes	No
Real-world device diversity	No	Yes
Geographic real data	Scripted locations	Actual user locations
Uptime SLA evidence	Yes	No
JavaScript error detection	Limited	Yes

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When to Use Each

Use synthetic monitoring when:

• You need continuous availability monitoring regardless of traffic levels
• You want proactive detection before users encounter issues
• You need uptime metrics for SLA reporting
• You want to test specific user flows (login, checkout, signup) reliably

Use RUM when:

• You want to understand real-world performance across user segments
• You need to identify issues affecting specific browsers or regions
• You want Core Web Vitals data for SEO and performance optimisation
• You have sufficient traffic to generate meaningful RUM data

Use both when:

• You're a high-traffic application where both proactive detection and real-world performance data are valuable
• Synthetic monitoring catches outages early; RUM reveals performance patterns and user-specific issues

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What About Simple Uptime Monitoring?

Simple HTTP uptime monitoring — checking that your URL returns 200 — sits within the synthetic monitoring category. It's the most basic form: a scripted check on a schedule.

Domain Monitor provides HTTP uptime monitoring and SSL/DNS checks — the synthetic monitoring baseline for availability. For more complex scripted flows, dedicated synthetic monitoring tools like Checkly or Datadog Synthetics add Playwright-based browser testing.

See what is black box monitoring for how both synthetic and RUM fit into the broader monitoring picture.

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Related Articles

• What Is Synthetic Monitoring?
• What Is Real User Monitoring?
• What Is Black Box Monitoring?
• What Is Website Monitoring?