field data
Performance measured from real visits, as opposed to a laboratory run.
What field data does not show
It is the more honest number and it does not exist for most small sites.
Where field data comes up on this site
- Core Web Vitals without CrUX: field data for small sitesThis guide explains why field data is missing, why lab data cannot fill the gap, and how to collect field data of your own that is honest about its sample size.
- Screaming Frog vs Sitebulb vs CrawlCheck: AI crawler auditsCore Web Vitals do not apply to crawlers at all: a crawler does not paint, scroll or click, and it does not count toward Chrome field data.
- Agent readiness checkers: Is It Agent Ready? vs CrawlCheckIts page-level sections describe the home page, and its Core Web Vitals come from Google’s public field data, so they are absent when Google has no sample for the site.
- Lighthouse scores vary between runs: two runs, 225% apartWhat about field data?
- Analytics added 650 ms to every request: how we found itWe added real-visit performance measurement so we could see field data for sites the Chrome UX Report will never cover.
Definitions that name field data
lab data · RUM · Server-Timing
Related terms in Delivery and rendering
What arrives on the wire, and what only exists after something else runs.
broken embed · payload ratio · render dependence · render dependence gap · edge cache pinning · TTFB · Core Web Vitals · CrUX · prompt injection · Hydration mismatch · Dynamic rendering · DOM depth · Edge transformation · 202 interstitial · rate limiting · bot management platform
Questions about field data
What is field data?
Performance measured from real visits, as opposed to a laboratory run.
What does field data not show or guarantee?
It is the more honest number and it does not exist for most small sites.
Which area of the glossary does field data belong to?
Delivery and rendering: What arrives on the wire, and what only exists after something else runs.
← CrUX · prompt injection →
See it in the full glossary · 772 terms across 19 areas.
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