The challenge
When Mercari, Japan's largest peer-to-peer marketplace, expanded to the United States, they faced a fundamental product problem: shipping.
Their Japanese model worked because it was invisible. Sellers picked a flat-rate tier based on weight, generated a prepaid label, and dropped off the package. No carrier accounts. No rate shopping. No errors. Mercari needed to replicate that exact experience for U.S. sellers who were equally unfamiliar with shipping, while integrating with multiple carriers, supporting discounted rates, and building infrastructure that could scale. Shipping had to feel like a natural part of the platform, not a separate workflow.
Building a direct USPS integration and tracking infrastructure in-house would have cost months of engineering time, pulled the team away from core marketplace development, and left them responsible for maintaining custom carrier-specific data pipelines indefinitely. They needed a shipping partner who could handle the infrastructure so they could stay focused on acquiring new customers and building the product.
The solution
Mercari integrated Shippo's API to power the entire shipping workflow behind their prepaid label system — address validation, label generation, USPS rate access, and tracking — all within the Mercari experience.
The tracking API proved especially critical. By normalizing tracking data across all major carriers into a single consistent format, Shippo eliminated the need for Mercari to maintain custom carrier-specific mappings, freeing the engineering team to focus on the marketplace rather than tracking infrastructure. Shippo's proactive carrier monitoring also surfaced disruptions early, giving Mercari's operations team the visibility to set accurate expectations before buyers and sellers were affected.
Shippo also gives Mercari ongoing visibility into how their sellers ship with detailed reports pulled directly from the API, plus industry benchmark data to assess performance against broader market standards. And Shippo continues to offer some of the best USPS discounts in the industry— along with the domain expertise to navigate carrier issues as they arise — keeping shipping costs low and operations running smoothly for both sellers and buyers.
The results
With the shipping architecture already mapped out, it took just one week for Mercari to fully integrate with Shippo and start shipping, a timeline that would have been impossible building direct carrier integrations from scratch.
9-12 months of engineering saved
By offloading tracking normalization across USPS, UPS, and FedEx to Shippo, Mercari avoided building and maintaining carrier-specific event parsers, webhook pipelines, and status mapping logic. Shippo's unified tracking schema and proactive carrier monitoring eliminated an entire category of ongoing infrastructure maintenance, freeing the team to focus on the marketplace.
250M+ shipments processed
Since launching in the U.S., Mercari sellers have processed over 250 million shipments through the platform. The vast majority of Mercari sellers use Mercari prepaid labels rather than arranging their own shipping, a strong indicator that the integrated experience is working and reducing friction.
2x year-over-year shipment volume growth
As Mercari has scaled U.S. operations, reliance on Shippo has grown proportionally, with shipment volume approximately doubling each year.