With Black Friday and Cyber Monday just weeks away, Catchpoint has identified the top five technical items most likely to cause web or mobile shopping sites to perform poorly.

When an online retail site is unavailable on a big shopping day, it is essentially the same as shutting the doors of a physical store

Every Black Friday-Cyber Monday weekend in the last decade has seen at least one major online retailer with web or mobile site outages or slowdowns. Memories of last year’s Black Friday problems, and Amazon’s Prime Day missteps this summer, should remind retailers that no company, big or small, is immune to interruptions or slowdowns in its sites’ digital experience.

Online retailers can learn from the mistakes of the past to optimally prepare and best position themselves for a smooth kick-off to the holidays.

The following elements are the most likely to cause slow load times or outages in the upcoming season:

1. Third Parties

These are site elements hosted by outside companies and beyond the direct control of the main site. One sluggish third-party component can slow down an entire web page. Example: in 2016 a high-end home goods retailer experienced very slow page load times intermittently on Black Friday due to problems with a third-party photo display service.

2. Regional View

If an online retailer monitors page load times only using national averages, it could be missing local or statewide performance problems. Example: in 2016 a major retailer experienced problems on its desktop site due to an ad tech provider, ultimately leading to ongoing site blackouts in Phoenix, starting early in the long holiday weekend.

3. Critical APIs

APIs are fundamental components of e-commerce sites, often supporting customer-facing, revenue-generating applications. Like third party services, popular APIs can come under major strain during peak traffic periods. If an API supporting payment options on a site breaks, an abandoned shopping cart will be the likely result.

4. Page Weight

One of the easiest ways to ensure faster load times is to make certain a site’s page weight (amount of data loaded into a shopper’s browser) isn’t too large. This is a technique large and small retailers often employ during peak traffic days, usually by eliminating excess images or graphics.

5. Server Scalability

The Amazon Prime Day outage was reported to be the simple result of overloaded servers. Load testing internal servers is one of the most straightforward, simple things one can do, as well as having additional servers on standby.

When an online retail site is unavailable on a big shopping day, it is essentially the same as shutting the doors of a physical store. And when your page load time slows, that’s the same as forcing a customer to stand in a long checkout line.

It’s important to remember that comprehensive monitoring from the end-user perspective is the definitive way to gain visibility into all the performance-impacting elements in the delivery chain, including those beyond one’s own firewall.