Reimporting Stripe's new OpenAPI spec into Mockoon left 559 routes on the old API

In March 2025, Stripe launched a new API version called "basil." This update moved certain fields from the parent subscription object to individual subscription items, specifically "current_period_start" and "current_period_end." As a result, any code that handles subscriptions began reading either of these fields.

When developers import Stripe's OpenAPI specification into Mockoon, a desktop tool for creating Stripe mock servers, the reimport process adds new routes without modifying or deleting existing ones. In this case, importing the basil spec resulted in the addition of two new routes, while 559 other routes remained unchanged. The reimport process simply adds new routes to the existing specification.

Before the basil update, Mockoon filled Stripe's text fields with empty strings. After the reimport, these empty fields were still present, which could cause issues with tests that relied on the data. To resolve this, developers had to manually edit the route responses to handle the empty values appropriately.

Mockoon's conversion of the OpenAPI spec into its own file format can be resource-intensive. The conversion process increased memory usage from 194 MiB (with Prism) to 487 MiB (with Mockoon), and start-up times were longer with Mockoon. However, the trade-off is that Mockoon provides a more straightforward way to create and manage mock servers when working with OpenAPI specifications.