"Do I need synthetic monitoring or real user monitoring?" — or both?
Synthetic monitoring uses automated checks (e.g. a service pinging your site every few minutes). Real user monitoring (RUM) collects data from actual visitors (page load time, errors, geography). They answer different questions and are often used together. This guide explains both, when to use each, and how they complement each other.
What Is Synthetic Monitoring?
Synthetic monitoring (sometimes "synthetic testing" or "proactive monitoring") means simulated requests to your site or API from one or more locations, on a schedule. A robot visits your URL (or runs a script) every 1, 5, or 10 minutes and records:
- Whether the request succeeded (e.g. HTTP 200).
- Response time (latency).
- Optional: status code, SSL validity, or content checks.
Because the checks are scripted and regular, you get:
- Consistent data — Same URL, same type of request, over time.
- Coverage when traffic is low — You see availability and speed even at 3 AM when no one is visiting.
- Alerting — If a check fails, you get notified (email, Slack, SMS) so you know your site or API is down or slow before users complain.
Most uptime monitoring or website monitoring tools are synthetic: they ping your endpoints and alert you when something's wrong. They don't depend on real user traffic.
What Is Real User Monitoring (RUM)?
Real user monitoring (RUM) means measuring what actual visitors experience when they use your site or app. A small script (or SDK) in your frontend collects data such as:
- Page load time (or time to interactive).
- Errors (e.g. failed requests, JavaScript errors).
- User context — Device, browser, country, page URL.
That data is sent to a RUM service, which aggregates it into dashboards and metrics (e.g. "p95 load time by country" or "error rate by page"). So you see:
- Real experience — Not a simulated check, but what users actually got.
- By segment — Performance for specific browsers, regions, or pages.
- Trends — How performance changes as you deploy or as traffic patterns change.
RUM does not run on a fixed schedule; it only has data when users are on your site. If traffic is zero, you get no RUM data — and no RUM-based alert that the site is down.
Synthetic vs RUM: Side-by-Side
| Synthetic monitoring | Real user monitoring (RUM) | |
|---|---|---|
| What it measures | Simulated requests from robots | Actual visits from real users |
| When it runs | On a schedule (e.g. every 1–5 min) | When users load your site |
| Good for | Uptime, availability, "is it down?" | Real-world speed and errors by segment |
| Works with no traffic | Yes | No — needs real traffic |
| Alerting | Yes — immediate when a check fails | Yes — when metrics cross thresholds |
| Typical use | "Is the site up? Is it responding?" | "How fast is it for users? Where do they see errors?" |
Neither replaces the other. Synthetic answers "is it up and responding?" 24/7. RUM answers "how did it perform for real users?" when they were there.
When to Use Synthetic Monitoring
Use synthetic monitoring when you need to:
- Know the moment your site or API goes down — So you can fix it before users notice. This is the core of uptime monitoring.
- Check availability 24/7 — Including nights and weekends when traffic may be low. RUM can't tell you the site is down if no one is visiting.
- Monitor specific URLs or APIs — Login, checkout, health endpoint, etc. You control what is checked and how often.
- Alert on SSL expiry — Many synthetic tools check certificates and alert before they expire.
- Compare regions — Run checks from multiple locations to see if the site is down or slow in one area only.
If you only add one form of monitoring, synthetic (uptime) monitoring is usually the first choice: it tells you when something is broken or unreachable, regardless of traffic.
When to Use Real User Monitoring (RUM)
Use RUM when you need to:
- See real user experience — Page load times, time to interactive, and error rates as experienced by visitors.
- Segment by device, browser, or region — e.g. "Is the site slow on mobile or in one country?"
- Correlate performance with releases — Did the new deploy slow down a specific page or segment?
- Prioritize fixes — Which pages or flows have the worst impact on users?
- Track Core Web Vitals or business metrics — Many RUM tools report LCP, FID, CLS, and custom timings.
RUM is complementary to synthetic: synthetic tells you "it's up and responding"; RUM tells you "it's fast (or not) for real users." RUM does not replace the need for synthetic checks to detect outages when traffic is low.
Using Both Together
Many teams use both:
- Synthetic monitoring — For uptime and availability. "Is the site/API up? Is it responding in under X seconds?" Alerts when checks fail so you're notified 24/7, even with no traffic.
- RUM — For real-user performance and errors. "How fast is it for users? Where do they see errors?" Use it to optimize and to catch issues that only appear for certain users or segments.
Together you get:
- Uptime and alerting from synthetic (so you never rely only on users to report downtime).
- Real-world performance and segmentation from RUM (so you know what to improve and for whom).
What About "Availability" in RUM?
Some RUM tools infer "availability" from error rates or failed requests. That's useful, but:
- If no one visits the site, RUM has no data — so it can't tell you the site is down.
- Synthetic checks run on a schedule, so they can tell you the site is down even when traffic is zero.
So for "is it up?" and 24/7 alerting, synthetic (uptime) monitoring remains the foundation. RUM adds "how did it perform for users?" on top.
How Webalert Fits In
Webalert is synthetic monitoring: we check your URLs (and optionally APIs, SSL) on a schedule from multiple locations and alert you when something fails or is slow. We don't collect data from your visitors' browsers — we simulate requests and measure response.
That makes Webalert the right tool for:
- Uptime and availability — Know when your site or API is down or slow.
- 24/7 coverage — Even when traffic is low or zero.
- SSL monitoring — Certificate expiry alerts.
- Status pages — Show status driven by those same checks.
For real user performance (page load by device/region, Core Web Vitals, front-end errors), you’d add a RUM product and use both: synthetic for uptime and alerting, RUM for real-user experience.
See features and pricing for what Webalert offers.
Quick Summary
- Synthetic monitoring = automated checks on a schedule. Answers "is it up? is it responding?" 24/7. Use it for uptime, alerting, and SSL.
- RUM = data from real visitors. Answers "how fast was it for users? where did they see errors?" Use it for performance and segmentation.
- Use both when you want uptime + alerting (synthetic) and real-user performance (RUM). Start with synthetic so you're never blind to outages when traffic is low.