The fastest checkout load is the one that starts before the shopper clicks checkout. Prefetching checkout scripts, styles, and payment SDKs while the shopper is still on the cart page can cut perceived checkout load time in half, and the implementation is a few lines of markup.

Prefetching Checkout Assets From the Cart Page: The Hidden Speed Lever

Most checkout speed work happens on the checkout page itself: lighter scripts, lazy-loaded sections, deferred pixels. That work matters, but it starts the clock when the shopper clicks checkout, which is the worst possible moment to begin loading. The shopper is at peak intent and peak impatience. Every millisecond of checkout load is a millisecond of doubt.

Prefetching flips the timing. While the shopper reviews the cart, adjusts quantities, and decides about shipping, the browser is idle between interactions. Those idle seconds are free load time. A handful of prefetch hints on the cart page can have the checkout's critical assets waiting in cache before the click, turning a two-second checkout load into something that feels instant.

What to prefetch

The candidates are the assets the checkout cannot render without: the payment provider SDKs, the checkout stylesheet and core scripts, and the address-autocomplete library if you use one. These are also the assets most likely to be slow, because payment SDKs are third-party, versioned remotely, and loaded with cache policies you do not control. Prefetching them from your own cart page puts the download under your timing instead of the shopper's patience.

Do not prefetch everything. Prefetching is a budget: every prefetched asset costs bandwidth and, on metered connections, the shopper's data. Limit it to the three to five resources that block checkout interactivity. The fraud-detection script that loads in the background can wait; the payment button SDK cannot.

The implementation

The basic version is resource hints in the cart page head: dns-prefetch for the payment provider domains, preconnect for the ones that need TLS handshakes, and prefetch for the specific script URLs the checkout will request. This is declarative, cheap, and supported everywhere that matters. It does not execute the scripts; it just warms the cache and the connections.

The sharper version is predictive: only prefetch when the shopper shows checkout intent. A hover on the checkout button, a focus on the button, or time spent on the cart page above a threshold can trigger the prefetch dynamically. This concentrates the bandwidth spend on shoppers who are actually going to check out, which is the polite version of the same trick.

What it is worth

The effect shows up in perceived load, not just measured load. Prefetching does not change the checkout's own resource count; it changes when the download happens. Time-to-interactive on the checkout drops because the blocking assets are already cached. On slow connections the difference is dramatic: a payment SDK that takes 800 milliseconds to fetch on 4G takes zero if it arrived during the cart review.

Measure it with field data, not lab tests. Prefetching's benefit depends on real connection behavior and real cart dwell time, both of which vary by device and market. Watch checkout bounce rate and payment-step completion in your analytics, segmented by device, before and after. The stores that benefit most are the ones with slow mobile connections and long cart reviews, which is to say most of them.

Checkout speed is usually optimized at the worst moment: after the click, under pressure. Prefetching moves the work to the best moment: before the click, during idle time. Add the resource hints to your cart page, prefetch only the blocking assets, and let the shopper's cart review pay for the checkout's load. It is the rare speed win that costs nothing in experience and buys time exactly when time matters most.

Frequently asked questions

What does prefetching checkout assets mean?

Loading the code, fonts, and other resources the checkout will need while the shopper is still on the cart page, so the checkout renders immediately when she proceeds instead of fetching everything at the moment of highest impatience.

Does prefetching help if the shopper never checks out?

The cost is some wasted bandwidth for shoppers who abandon the cart. Kept to the critical checkout assets, that cost is small next to the completion gain from a checkout that appears instantly.

What should be prefetched first?

The checkout's critical path resources: its main scripts and styles, fonts used above the fold, and the payment interface's early assets where the platform allows. Images and below the fold extras can wait.