# What do visitors on slow 3G see while personalized content loads?

Asked by greta on 2025-08-19. Tags: performance, dx, fallbacks.

Hello, I build for an audience in Nairobi where a large share of sessions
arrive on slow or unstable connections, so I test everything throttled to slow
3G in devtools before shipping.

Before adopting personalization I want to understand the worst case precisely.
I ruled out the usual client-side testing tools because their anti-flicker
snippets hide the whole page while the script loads, which on a throttled
connection is a very long blank screen. My question for Croct: what exactly
does a slow 3G visitor see in the server-side mode, and in the client-side
mode? And is there any scenario where a user gets stuck waiting indefinitely?
Thank you kindly.

## 1 answer

### Accepted answer from Croct Bot (2025-08-19)

The two modes behave quite differently on a throttled connection, and
neither of them can strand a visitor indefinitely.

Server-side: the content is resolved before the HTML is sent, so a slow 3G
visitor downloads exactly one page that already contains the right content.
There is no second round trip to fetch and swap anything in, which means slow
connections pay only their normal page-download cost. This is the mode I
would recommend for your audience.

Client-side: the page renders immediately and the slot content is fetched
over the network, so the worst case is bounded by two things. Every fetch
takes a [fallback](https://docs.croct.com/explanation/content/fallback-content), and a timeout caps the wait: `defaultFetchTimeout` defaults
to 5000ms in the JavaScript SDK and 2000ms in Next.js, and you can set it
lower. When the timeout fires, the default content renders. So the worst
case on slow 3G is "default content after your configured wait", never a
spinner that spins forever and never a hidden page.

For contrast, the architecture you ruled out hides the page for up to the
snippet's timeout on slow connections, commonly 3 to 4 seconds (Google
Optimize defaulted to 4s). That entire class of delay does not exist here
because nothing is ever hidden while waiting for a script.