Cart Performance at Scale: Crystallize Shop API Under Black Friday Load

Black Friday (and other major campaign peaks) puts enormous pressure on an eCommerce stack — slow carts, failed checkouts, or downtime translate directly into lost sales and frustrated customers. That’s why we decided to push the Crystallize Shop API to its limits, simulating real-world traffic at scale and full checkout flows.

The Shop API powers the cart, checkout initiation, and order completion logic — it is in effect the heartbeat of your storefront. On peak days, every millisecond and every failed request matters: APIs can bottleneck, databases can lag, and throughput limits get exposed.

Our tests were designed to provoke those failure modes and determine whether the system can withstand pressure.

We're happy to share that Crystallize can handle cart interactions, even during major retail events like Black Friday.

We simulated a realistic customer journey through the cart and checkout:

• Cart hydration: Every request added items to a cart.
• Checkout initiation: 50% of carts progressed to the checkout stage.
• Order completion: 60% of those resulted in a completed order.

This means that 30% of all carts are converted into orders, which aligns with healthy B2C benchmarks. Successful eCommerce operations often achieve cart-to-order rates of 25–30%, while anything below 20% is typically a sign of friction.

During the tests, we streamed real-time cart and checkout statistics. At scale, the dashboards were blinking with activity, making it visually clear how fast carts were being processed. For operations teams, this kind of visibility ensures confidence in the system’s ability to withstand sudden bursts of traffic.

In our scale test, the Crystallize Shop API consistently handled heavy cart activity. Each simulated request resulted in an average of 1.8 cart API calls, which pushed peak throughput to over 500 cart operations per second. That equals more than 1.8 million cart write interactions per hour, proving the API is ready for the demands of Black Friday–level traffic.

Test setup:

• Test tool: K6 from Grafana
• Queries per request:
• • Minimum 1 hydration query
  • 50% included 2 queries
  • 60% of those included 3 queries (Hydrate, Place, Complete Order)
• Effective load: Each request = 1.8 cart API calls

Peak performance:

• Requests per second (write load): 281.3
• Adjusted cart API calls per second: 506.4
• Equivalent per hour: just above 1.8 million cart write API calls

When Black Friday arrives, retailers need more than hope—they need a system that won’t crack under pressure. For shoppers, Black Friday should not mean waiting in line.

Happy to report Crystallize delivers what’s needed. It scales effortlessly to handle millions of cart operations per hour so businesses can face surging traffic with confidence (and without waiting in line for shoppers).

Rather than losing revenue to crashes or timeouts, high throughput ensures spikes in visitor volume translate into real sales, not abandoned carts.

We also measured conversion realism: the cart-to-order ratios in our test fell squarely within healthy industry norms, validating not just raw performance but also the viability of the purchase flow itself. And through all of this, robust real-time monitoring kept operations teams in control—displaying live metrics so they could detect and respond to anomalies instantly during high-stakes campaigns.

For B2C and B2B retailers, the cart is the beating heart of the customer journey. Performance at scale is not optional; it’s revenue critical. With the Crystallize Shop API, you’re equipped to deliver reliable, fast, and scalable commerce experiences that thrive under pressure.

SCHEDULE 1-on-1 DEMO to explore how Crystallize can help you achieve your goals. Or, why not START building for FREE.