Lightning CMP is built so the banner costs you nothing measurable in Core Web
Vitals — a 100/100 Lighthouse score **with the banner running** is the design
target, not a best case.

## Why it's fast

- **~12 KB gzipped**, loaded `async` — never render-blocking.
- **Shadow-DOM UI** — the banner's styles are fully isolated, so there's no
  layout thrash against your page CSS.
- **Off-critical-path loaders** — [bridges](/integrations/bridges/) inject vendor
  scripts at idle time, after first paint.
- **Edge-resolved config** — one round-trip to a warmed connection
  (`preconnect`), not a chain of blocking requests.

## Keep it fast

- Keep the `preconnect` in the snippet.
- Don't move the CMP `<script>` out of `async`, and don't let a defer-all
  optimiser touch it (that hurts both correctness _and_ timing — see
  [Troubleshooting](/guides/troubleshooting/)).
- Prefer [bridging](/integrations/bridges/) Google over hard-blocking it — the
  bridge loads off the critical path with correct ordering.

:::note[More detail coming]
CWV measurements and guidance are being migrated from `docs/INSTALL.md` §
_“Performance & Core Web Vitals.”_
:::