If you sell on Amazon and on your own website (or on eBay, Walmart or a physical store), keeping stock levels accurate by hand quickly becomes impossible. Overselling leads to cancellations and account health issues; underselling leaves money on the table. The solution is to automate inventory sync with Amazon's Selling Partner API (SP-API).
What SP-API can do for you
- Update available quantity for your listings automatically
- Download new orders and push them to your store, ERP or warehouse
- Update prices based on your own rules
- Create and update listings in bulk
- Pull reports for sales, fees, FBA inventory and settlements
A typical sync architecture
- One source of truth. Decide where stock is "owned" — usually your ERP, warehouse system or main store (Shopify, WooCommerce, Odoo).
- Change detection. Listen for stock changes using webhooks from your store or a scheduled check.
- Queue. Put updates into a queue so spikes and API limits do not cause lost updates.
- Amazon update. Send quantity changes to Amazon through the Listings Items API or feeds for bulk updates.
- Order import. Poll or subscribe to order notifications, then reduce stock everywhere else.
- Logging & alerts. Record every change and alert your team when something fails.
Things to plan before you build
SKU mapping
Your store SKUs and Amazon seller SKUs must match — or you need a mapping table. Bundles and variations need special care.
Safety stock
Keep a small buffer so that orders placed at the same moment on two channels do not oversell.
Rate limits
SP-API applies rate limits per operation. A good integration batches updates, retries with back-off and never "hammers" the API.
FBA vs FBM
Fulfilled-by-Amazon stock is managed by Amazon; merchant-fulfilled stock is managed by you. Your sync rules should treat them differently.
Security & access
Register the application correctly, store credentials securely and give it only the roles it needs.
Build vs buy
Off-the-shelf multichannel tools work well for standard setups. A custom integration makes sense when you have unusual SKU structures, your own ERP, specific pricing rules or high order volumes where subscription fees add up.
Moving from MWS
Amazon's older MWS API has been retired. If you still run legacy tools built on MWS, they need to be migrated to SP-API to keep working.
The goal is simple: one stock number, updated everywhere, without anyone touching a spreadsheet.
We build Amazon, eBay, Shopify and Odoo integrations every month. Hire an Amazon & eBay API developer or read about our API integration services.