Nintendo 3ds Serial Number Lookup Page

If you want to play Japanese games on a US console, you need to remove the region lock via hacks. Before purchasing a Japanese 3DS (JE prefix), you should perform a serial number lookup to ensure the console firmware version (which is loosely tied to serial manufacturing dates) is hackable. Pre-2014 serials are generally safer.

Nintendo used to allow direct lookups on their support site. Nintendo 3ds Serial Number Lookup