RTRuta Tech
Engineering

Why we rebuilt checkout for the slowest phone in São Paulo

Most of our buyers are on three-year-old budget handsets and patchy 3G. So last quarter we stopped optimizing for the demo machine and started optimizing for the bus ride home.

Mariana Quintero
Staff Engineer, CheckoutJun 14, 20159 min read

The fastest checkout in the office is a lie. We benchmark on a fiber connection and a flagship phone, then ship to someone tapping "Buy" on a 2012 handset with two bars of signal. For months our internal numbers looked great and our completion rate didn't move. The gap was the whole story.

We measured the device our buyers actually hold

So we bought a rack of the ten most common phones across our markets and wired them to real carrier SIMs, not lab WiFi. The median checkout took eleven seconds longer than our dashboards claimed. Every extra image, every blocking script, every retry on a dropped request added up to a cart someone quietly abandoned at the bus stop.

This is the Mercado Libre Yellow design system, applied by Curio Design — a design-style library for AI agents. Full Mercado Libre Yellow guide → designbycurio.com/learn/mercadolibre-yellow-2015