Perf monitoring — Vercel Speed Insights as RUM

Vercel Speed Insights for RUM Web Vitals site, complementing Cloudflare's edge-measured metrics and Sentry's API traces. Free, no Vercel hosting required.

Perf monitoring — Vercel Speed Insights as RUM

Decision

Every family site ships Vercel Speed Insights as the Real-User Monitoring (RUM) layer for Web Vitals. The client script (@vercel/speed-insights) loads from @chirag127/oriz-kit behind a per-site env-var toggle (ENABLE_SPEED_INSIGHTS=true|false). Vercel hosting is not required — the script works on Cloudflare Pages (the family’s primary host).

This pairs with two existing perf signals:

• Cloudflare Web Analytics — server-side / edge-measured
• Sentry Performance — sampled API + Worker traces
• Lighthouse CI — lab-only, in PRs

Together = full perf picture.

Why

• Web Vitals are the only perf signal Google ranks SEO on. Lab metrics (Lighthouse) miss real users; edge metrics (Cloudflare) miss client-side layout shift and interaction lag.
• Speed Insights is RUM — captures LCP, INP, CLS, FCP, TTFB from real visitors on real devices and real networks. The only one of our perf tools that does this.
• Cloudflare Web Vitals is server-side — measured at the edge, tells us what the network delivered, not what the user saw. Misses CLS entirely (CLS happens after paint).
• Sentry Performance is trace-focused — great for “why is this API slow” but its JS Web Vitals capture is sample-based and less detailed.
• Free with no card. 10K data points/month per project; per-site env-var toggle keeps low-traffic sites silent for headroom.
• Vendor-neutral — the underlying library is web-vitals (W3C standard), so swapping Speed Insights for a self-rolled endpoint is mechanical.

Implications

Architecture

• @chirag127/oriz-kit exports injectSpeedInsights() behind the ENABLE_SPEED_INSIGHTS env var.
• Each site has its own Vercel project ID for Speed Insights; project IDs land in Doppler and sync to Cloudflare Pages env vars at build time.
• @vercel/speed-insights registers a CSP connect-src entry for vitals.vercel-insights.com — added to the security-headers preset.

Quota strategy (never-hit-quotas)

• 10K data points / project / month is generous for low-traffic sites; high-traffic sites (oriz-blog-site, oriz.in apex) may need the toggle off until usage is understood.
• Per-site ENABLE_SPEED_INSIGHTS=true|false env var (mirrors the Sentry pattern) prevents a runaway visitor spike from burning the quota.
• Per-page sampling can be configured via injectSpeedInsights({ sampleRate: 0.5 }) if a single site’s traffic outgrows the cap.

Three perf layers, each in its own tool

What we don’t do

• No DebugBear / SpeedCurve / Calibre — Speed Insights covers RUM free; lab is covered by Lighthouse CI.
• No self-rolled endpoint — re-implementing dashboards / alerts costs more than the Speed Insights free tier.
• No card-on-file at Vercel — free tier sign-up is GitHub OAuth.
• No Vercel hosting — Cloudflare Pages stays primary host.

Cross-refs

• Vercel Speed Insights service entry
• perf services index
• Sentry — error tracking + perf traces
• Cloudflare Web Analytics
• Lighthouse CI — lab-only score in PRs
• Cloudflare Pages — primary host
• Never hit quotas rule
• No card-on-file rule

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