Affiliate sites tumble in SERPs when performance drops, iGaming operators watch deposits fizzle out, and eCommerce brands bleed sales. Yet many teams still benchmark from the comfort of office fibre connections.
Real customers are on ageing phones, throttled 4G, or patchy subway Wi-Fi. If the page shifts under their thumb or takes more than a heartbeat, they leave.
Core Web Vitals are field metrics (real users), not your best laptop.
RUM (Real-User Monitoring) shows what’s actually broken, where, and for whom.
Use field data to prioritize, and lab tools to reproduce and debug.
Fast wins usually come from LCP (images/fonts), INP (JS + third parties), and CLS (layout shifts).
Speed is still one of the cleanest “silent” growth levers: it affects rankings, paid efficiency, and conversions at the same time.
Typical patterns teams see:
when mobile load time jumps, bounce climbs
when checkout/signup feels laggy, conversion drops
when pages shift around, users lose trust and stop clicking
In iGaming the penalty is immediate: slow registration or deposit flows cause drop-offs before the funnel even starts, plus extra strain on support and payments.
Bottom line: performance isn’t a nice-to-have — it’s revenue protection.
Core Web Vitals track three user outcomes:
| Metric | “Good” threshold | What it measures | Common causes |
|---|---|---|---|
| LCP | ≤ 2.5s | main content load speed | heavy hero images, render-blocking CSS/JS, slow server |
| INP (replaced FID) | ≤ 200ms | interaction responsiveness | long tasks, too much JS, third-party scripts |
| CLS | ≤ 0.10 | visual stability | late images/fonts/ads, injected UI |
Note: INP replaced FID, so make sure your dashboards and tools track the right metric.
Lab tools (Lighthouse, DevTools traces) are great for debugging and catching regressions.
But they don’t reliably simulate:
low-end CPUs
weird cache states
flaky networks
third-party scripts firing at scale
real user flows across many pages
Field data (RUM) shows what’s actually happening to customers.
Use this workflow:
RUM finds the biggest business-impact failures (high traffic + bad p75).
Lab tools reproduce and explain the root cause (so you can fix it).
If you only use lab tests, you’ll often “fix” things that weren’t hurting you — and miss the ones that are.
Tag managers and ads bloating the main thread → INP gets worse
Unoptimized hero images → LCP fails on mobile
Client-side-only rendering → blank screens on weaker devices
Third-party scripts loading synchronously → interaction delays
Late-loading CSS/JS shifting CTAs → CLS spikes
In a recent audit, mobile users waited 5+ seconds to load a sportsbook signup page on 3G in rural UK. Drop-off before reaching the offer cost an estimated $7k/day in deposits (internal estimate, 2025).
The pattern is common:
the damage concentrates on mobile + weak networks
you lose users before analytics events even fire
Best when you want dashboards and segmentation without building your own pipeline.
Look for:
LCP/INP/CLS with p75 reporting
breakdowns by page group/template
segments by device + connection
release markers (so you can spot regressions)
Examples teams often use:
DebugBear (RUM)
Sematext / Raygun (depending on your stack)
Useful for quick checks:
PageSpeed Insights (CrUX field data when available)
Chrome DevTools Performance panel
Install the open-source web-vitals library and send metrics to your analytics stack.
Minimum viable setup:
capture LCP/INP/CLS
send URL + template + device + connection + release version
report p75 by key landing pages and funnel steps
alert on meaningful regressions for high-traffic pages
Most LCP failures come down to one thing: your hero element is too heavy or too late.
Quick wins:
compress + serve AVIF/WebP
preload the true LCP image
remove render-blocking CSS where possible
cut unnecessary JS before content renders
improve caching and TTFB (CDN/edge where it makes sense)
Rule: identify the LCP element and treat it like a core product requirement.
INP usually fails because the main thread is overloaded.
Quick wins:
reduce bundle size and unused JS
break up long tasks (especially on interaction handlers)
defer or gate third-party scripts (chat, experiments, trackers)
avoid heavy client-side rendering on critical routes
Rule: if tapping feels delayed, it’s almost always JS + third parties.
CLS problems are often caused by “helpful” UI that shows up late.
Quick wins:
reserve space for images/iframes (set dimensions or aspect ratio)
use font-display: swap and preload critical fonts
stop banners/cookie bars from pushing content down
stabilize ad slots with fixed containers
Rule: CLS usually comes from one global component that hits every page.
Serve next-gen images (AVIF/WebP), lazy-load below the fold
Preconnect and preload only truly critical assets
Use font-display: swap and limit font variants
Defer non-critical JS, split bundles, load routes with import()
Prefer SSR/SSG for landing pages and funnel entry points
Add a performance budget in CI to catch regressions
Start with top landing pages + signup/checkout/deposit flows
Segment by mobile vs desktop and slow networks vs Wi-Fi
Prioritize by traffic × conversion sensitivity × CWV severity
Fix one bottleneck at a time and mark releases
Track p75 trend, not averages, and verify gains where it matters
Is speed still a ranking factor after Google’s 2024 updates?
Yes. Page experience signals (including Core Web Vitals) still matter, especially when relevance is similar across results.
My Lighthouse score is good. Why do real users still fail CWV?
Because real users have slower devices, throttled networks, third-party scripts, and messy cache states that lab tests don’t fully reproduce.
Do I need both CrUX and RUM?
If you can, yes: CrUX helps for external benchmarks; RUM is what helps you prioritize, segment, and tie performance to revenue.
If you want a second set of eyes, we can run a 7-day real-user Core Web Vitals report and send you a prioritized action plan.
Send your URL and we’ll reply with:
the pages and segments failing CWV (p75)
what’s causing the drops (LCP/INP/CLS drivers)
the fixes that will move revenue fastest