testland/rum-to-synthetic-gap-analyzer
Reads Real User Monitoring data (Datadog RUM, Sentry Performance, GA4 Core Web Vitals / CrUX) to identify high-traffic user journeys that have no synthetic monitor coverage: ranks journeys by session volume times business value, diffs the ranked list against existing synthetic monitors, and emits a prioritized gap list ready to feed into synthetic-monitor-author. Use when an observability stack has RUM instrumented but the team suspects synthetic coverage is sparse, biased toward low-traffic paths, or was never systematically derived from real usage data.
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rum-source-queries.mdreferences/
RUM source queries
Per-source instructions for pulling the top-N journey inventory (Step 1 of
rum-to-synthetic-gap-analyzer). Aim for the top 50 view paths (or transaction
names) by session volume to avoid chasing long-tail pages with negligible traffic.
Datadog RUM
In the RUM Explorer (https://app.datadoghq.com/rum/explorer):
- Set event type to Views.
- Group by
@view.url_path(or@view.namefor SPAs with named routes). Per Datadog RUM Explorer docs, "aggregate into groups based on the value of one or several event facets" and "extract the count of events per group" to get session volume per path. - Sort descending by count. Export as CSV or copy the top-50 rows.
- For each path, also note the p75 LCP / p75 CLS available in the Performance Overviews dashboard (Datadog RUM Dashboards: "See a global view of your website/app performance and demographics").
Query syntax shorthand: @view.url_path:* | count by @view.url_path | sort desc.
RUM Explorer supports key:value pairs where custom attributes require a
created facet first (Datadog RUM Search).
Sentry Performance
Open the Performance module and use the Trace Explorer to slice by transaction name. Per Sentry Transaction Summary docs, the platform surfaces throughput as TPM (transactions per minute) and TPS (transactions per second) per named transaction. Sort by Total throughput to surface highest-volume journeys. Export the table.
GA4 + CrUX (public-facing sites)
For public pages, the Chrome User Experience Report provides origin-level and
URL-level field data. Per CrUX methodology, pages must be
publicly discoverable (HTTP 200, no noindex) and meet a minimum visitor
threshold for statistical confidence; exact threshold is undisclosed. Access
via:
- CrUX API (
https://chromeuxreport.googleapis.com/v1/records:queryRecord) for per-URL LCP, INP, CLS distributions. - BigQuery (
chrome-ux-report.all.<YYYYMM>) for bulk URL-level data. - PageSpeed Insights API for per-URL field vs. lab comparison.
Per web.dev Core Web Vitals, the three stable metrics are:
- LCP (Largest Contentful Paint): good threshold 2.5 s.
- INP (Interaction to Next Paint, replaced FID in 2024): good threshold 200 ms.
- CLS (Cumulative Layout Shift): good threshold 0.1.
All thresholds apply at the 75th percentile of page loads (web.dev CWV). CrUX field data is "the Google dataset of the Web Vitals program" (CrUX docs).