Methods
Lab data vs field data
Lab data comes from a controlled test; field data comes from real visitors. Both matter, for different reasons.
Lab data is reproducible: same device, same network, same steps, so it is perfect for debugging and CI. But one machine cannot represent every visitor, so it can look rosy while real users struggle.
Field data is messy and honest: it captures the full range of devices and connections in the wild. Core Web Vitals are officially assessed on field data. The healthiest workflow uses lab data to prevent regressions and field data to confirm the real-world result.
Related terms
- RUMReal User MonitoringMeasuring performance from the browsers of your actual visitors, on their real devices and networks.
- Synthetic MonitoringScheduled, repeatable tests that load a page in a controlled environment on a fixed interval.
- LighthouseGoogle's open-source tool that audits a page in a lab run and scores performance, accessibility, SEO and more.
- CrUXChrome UX ReportGoogle's public dataset of real-world Core Web Vitals, aggregated from opted-in Chrome users.
- p75Percentile (p75)The value below which a given share of visits fall. p75 means 75 percent were at least this fast.
- Web Vitals AttributionThe extra diagnostic data that explains why a metric was slow, not just how slow it was.
- Web AnalyticsTraffic and behaviour measurement: page views, visitors, referrers and journeys, alongside performance.
- Error TrackingCapturing JavaScript errors and failed requests from real sessions, grouped so you see the real problems.
- AlertingNotification rules that tell you when a metric breaches a threshold or degrades, before customers complain.
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