I was invited to improve the stability and performance of the legacy Magento 1 codebase.Allowed to onboard more sellers and sell more products by improving the import engine: adding filtering options and fixing bugs. Reduced time-to-market for import features by refactoring, simplifying, and writing tests for the import engine. Reduced seller churn by stabilizing the import engine. Added useful product import statistics to the logs. Improved import developer experience by making local imports run faster with caching and stub image mechanisms.Optimized product pages load time by 600%, from 4000 to 600 ms. Made errors and performance profiles visible by integrating New Relic. Fixed broken Magento reindex so that more products became available. Added project documentation for managers and developers.