Core Web Vitals & PageSpeed
Automatic daily monitoring of all 6 Core Web Vitals for mobile and desktop. Track trends, catch regressions, and share Google audit links with clients.
How it works
SiteBrief uses the Google PageSpeed Insights API to run a full Lighthouse audit on your site every day at 3:00 AM. Results are stored for both mobile and desktop strategies, so you can track performance trends over time.
To enable it: go to the site detail page → Settings → turn on Core Web Vitals monitoring. The first results appear after the next daily check, or you can trigger it manually via the cron API.
What gets measured
| Metric | Abbr | What it measures | Good threshold |
|---|---|---|---|
| Largest Contentful Paint | LCP | Time until the largest visible element loads | < 2.5s |
| Cumulative Layout Shift | CLS | How much page elements move unexpectedly during load | < 0.1 |
| Interaction to Next Paint | INP | Response time to clicks, taps, and keyboard input | < 200ms |
| First Contentful Paint | FCP | Time until any content first appears on screen | < 1.8s |
| Time to First Byte | TTFB | How fast the server responds to the first request | < 800ms |
| Total Blocking Time | TBT | Total time JavaScript blocks the main thread during load | < 200ms |
Score ranges
| Score | Rating | What it means |
|---|---|---|
| 90–100 | 🟢 Good | Fast site. All or most Core Web Vitals are in the Good range. |
| 50–89 | 🟡 Needs improvement | Some performance issues. Worth investigating. |
| 0–49 | 🔴 Poor | Serious problems. Likely affecting SEO and user retention. |
Mobile vs Desktop
SiteBrief checks both strategies. Google uses mobile-first indexing — mobile scores are what affect SEO rankings. Desktop scores are typically 10–20 points higher and are useful for comparing the experience across device types.
Use the Mobile / Desktop toggle on the site detail page to switch between the two views.
14-day trends
Each metric card shows a sparkline of the last 14 checks. The color reflects the current rating: green for Good, amber for Needs improvement, red for Poor. A downward trend (lower values) is good for time-based metrics (LCP, FCP, TTFB, INP, TBT) and for CLS.
If you see a sudden spike in LCP overnight, it usually means a large image was uploaded, a plugin was updated, or the server is under load.
View audit link
Any metric that is not in the Good range shows a View audit → link. Clicking it opens Google PageSpeed Insights with a full Lighthouse report for that URL and strategy — with specific, actionable recommendations from Google.
This is useful when a client asks "why is my score low?" — send them the audit link directly instead of trying to explain it yourself.
In client reports
The PDF report includes a full Core Web Vitals section on page 2: performance score gauge, all 6 metrics with Good/Needs improvement/Poor ratings, and security status. The report is generated with the latest stored data — run a manual check before sending if you want fresh results.
Low CWV scores are a natural upsell opportunity — the data gives you a concrete, Google-backed reason to discuss a performance optimization engagement with the client.
Common reasons for low scores
- Large unoptimized images (LCP) — use WebP, compress, add explicit dimensions, preload the hero image.
- Render-blocking resources (FCP, TBT) — defer non-critical JS, inline critical CSS.
- Slow server response (TTFB) — add server-side caching, use a CDN, or upgrade hosting.
- Layout shifts (CLS) — images without
width/height, late-loading ads, web fonts causing FOUT. - Heavy JavaScript (TBT, INP) — code-split, lazy-load, remove unused plugins.
- No CDN — serving from a single origin far from the user. A CDN can cut TTFB and LCP dramatically.