A theme demo uses a controlled catalog and polished assets. Test your own products, menus, filters, apps, and mobile images before calling it fast.
Duplicate the live theme. Change one thing, use the same page and device, and record what happened. If the change breaks a customer path, roll it back before touching production.
Check the home, collection, product, cart, and checkout path on a phone. Confirm the page still works with a slow connection and that the business owner for the feature agrees it can change.
A theme demo uses a controlled catalog and polished assets. Test your own products, menus, filters, apps, and mobile images before calling it fast.
Source: Shopify theme performance guidance. Reviewed Sep 22, 2026.