# How to Sync Products Stock Inventory Between Online Stores and Business Apps?
# What is stock inventory?
Digital stock inventory is used by businesses to keep track of physical product counts throughout business processes. Most of the modern online shops, ERP and eCommerce systems, or other business apps have this feature built-in. It's key for business activity to make sure inventory is always correctly set and synced with the online shop.
SyncPenguin can be used to set up two-way or one-way synchronization of product inventory between multiple popular eCommerce platforms, online stores or ERP systems.
# How does the sync work?
By default, the sync matches products between multiple apps using their SKU values. For example, if you have a product (or product variant) named 'Apple iPhone 11' with SKU equal to 45381 in Shopify, and a catalog item 'iPhone 11' in Square with SKU equal to 45381, SyncPenguin treat those products as matching, and sync the inventory between them.
Note that our platform is flexible and allows us to customize any aspect of the synchronization. The products can be matched by names, custom IDs, or in any other way. You can also filter out which SKUs should be synced and which not, in case you don't want all products to get synced.
Once the products are matched, there are two basic ways of how to perform sync: mirroring and adjustment sync.
# 1. Mirroring
Mirroring ensures that inventory count exactly matches between business apps. No matter how inventory changes in one place, it should always be synced with the other, and corresponding counts should coincide.
Note that in this case, if initially, the quantities are different, they need to be synced from one tool to another in order to avoid losing any actual important data.
# 2. Adjustment sync
Adjustment sync works a little bit differently. Instead of syncing the actual availability counts to make sure they are the same, it ensures that all adjustments that are made in one place are also made in the other place. For example, if 5 items of some product were sold in your online store, than those 5 items need to be subtracted from the availability count in Square. Note that it doesn't mean that those counts are the same: we just track what changes are made and reflect them to both service.
# What services are supported?
Currently we have connectors to Shopify, Square, BigCommerce, WooCommerce, Shopware and QuickBooks. This allows us to provide you with synchronization of those tools in a highly customizable way that'll fit your business. If you are interested in synchronization of inventory or product catalogs, please leave us a message below with a short explanation of what you're looking for: