RUM vs. synthetic monitoring: which one catches a broken checkout?
Real-user monitoring and synthetic checks are often pitched against each other. For a checkout they answer different questions, and the gaps in one are exactly where the other is strong.
What real-user monitoring sees
RUM collects data from actual visitors: page timings, Web Vitals, JavaScript errors, conversion funnels. It reflects every device, network and browser your customers really use, which no test can match. It is the right tool for "is checkout getting slower on mobile" or "which step do people abandon".
Where it goes quiet
RUM needs traffic. At 3 a.m., on a low-traffic market, or right after a deploy on a quiet day, there may be too few checkouts to tell a failure from a normal lull. And a checkout that is fully broken produces the weakest signal of all: nobody completes it, so the funnel just shows fewer orders — the same shape as a slow sales day.
What synthetic checks add
A synthetic check runs on a schedule whether anyone is shopping or not. It uses the same product, address and path each time, so a change in result means the store changed, not the traffic. And because it knows what it expected at every step, it can say exactly what went wrong — no shipping methods, a wrong total, a payment step that never rendered — instead of "conversion dropped".
Side by side
Data source: RUM measures real visitors; synthetic monitoring runs a scripted visitor of its own. Coverage: RUM sees every device and network your customers use; a synthetic check sees one browser on one path, the same every time. Timing: RUM reports when traffic arrives; synthetic checks report on a schedule, day and night.
Diagnosis: RUM tells you that a metric moved; a synthetic check tells you which step failed and what it saw there. Setup: RUM needs a script on every page; a synthetic check needs nothing installed on the store, only the address.
Which one to start with
For a store with a few dozen orders a day, start with synthetic checks. At that volume a broken checkout and a quiet afternoon look the same in RUM, and the first priority is knowing within minutes that nobody can buy.
Add RUM when traffic is high enough for trends to mean something, and the questions move from "does it work?" to "is it fast enough on mobile, and where do people drop off?".
Use both
Synthetic checks answer "can someone buy right now?" and alert within minutes. RUM answers "how is buying going for real customers?" and shows trends. A store that relies only on RUM finds outages late; a store that relies only on synthetic checks misses problems that only affect certain devices. Together they cover each other’s blind spots. Related: why uptime monitoring misses broken checkouts and how to monitor a WooCommerce checkout.
Check your own store now, free: the WooCommerce checkout checker or the Magento checkout test walks the checkout in a real browser and shows the step where it stops.
Common questions
What is the difference between RUM and synthetic monitoring?
RUM measures what real visitors experience on their own devices. Synthetic monitoring runs a scripted visit on a schedule, so it works with no traffic and can say exactly which step failed.
Can RUM detect a broken checkout?
Only indirectly. A fully broken checkout produces no completed purchases, which in RUM looks like fewer orders, the same as a slow day. On busy stores that drop shows quickly; on small ones it can take hours.
Do I need both?
Larger stores usually run both: synthetic checks to know at once when buying breaks, RUM to see speed and drop-off across real devices. A small store gets more from synthetic checks first.