The eBay Sandbox is a self-contained virtual testing environment that mimics the live eBay Production environment.
The Sandbox provides a shielded space where you can test your application by watching it process mock eBay transactions generated by your requests to the eBay APIs without touching any live eBay listings, user accounts, or bank accounts. Testing in the Sandbox gives you the ability to fully test and debug your eBay API routines before you run them in eBay's live production environment.
Testing in the Sandbox has many advantages over testing in the Production environment. Because all transactions in the Sandbox use mock currencies, you can list and re-list items in bulk, and complete sales transactions without having to pay real fees to eBay and without incurring any obligation to deliver real items to real buyers.
Note: As you test your application, be sure to review the guidelines outlined in Compatible Application Check and the Checklist for Going Live to ensure you meet the requirements for moving your application into the live eBay production environment.