FNSKU Format Checker

FNSKU mix-ups are quiet killers. The worst one I saw: a seller used the manufacturer's UPC barcode instead of Amazon's FNSKU, and Amazon commingled his inventory with every other seller carrying the same product. When a customer got a counterfeit from a different seller, the complaint landed on his account. Commingling means you own the defects you didn't make.

Your FNSKU is the label Amazon assigns to your unit so it tracks your stock separately. It's a specific format — ten characters, letters and numbers, no spaces, no symbols. This checker confirms a code fits that shape before you print it, so you don't slap a bad label on a box heading to FBA.

What it checks

Two things, and both matter:

• Length. A real FNSKU is exactly ten characters. Nine or eleven means you dropped or added a digit, and the label won't match Amazon's record.
• Character set. Only A–Z and 0–9. A stray space or dash means the scanner may read it wrong or not at all.

If either fails, the tool tells you exactly which. You don't have to guess whether the problem is length or a bad character.

Why the label must be right

At the fulfillment center, a scanner reads that code and decides whose inventory this is. A wrong FNSKU can land your unit in someone else's bin, or leave it uncounted while you think you're in stock. Either way you lose visibility, and visibility is the whole point of FBA.

Use it in your prep step

If you label products yourself or hand a prep list to a VA, run every new FNSKU through this check before printing. It's faster than discovering the mistake after a shipment goes inert. Copy the code straight from Seller Central, paste it here, and only print once it reads valid.

A valid format doesn't prove the code belongs to the right product — check that against the listing too. But a bad format proves it's wrong, and that's worth catching first.