# Product identifiers Product identifiers are the values that let a sales channel recognise that your listing and someone else's describe the same physical product: a GTIN, or a manufacturer part number together with a brand. They matter because a channel that can identify a product can attach reviews, specifications and competing offers to it, and one that cannot has to treat your listing as an unknown object. - **Canonical URL:** https://www.feedlab.io/knowledge/concepts/product-identifiers - **Last reviewed:** 16 September 2026 - **Source:** feedlab knowledge base - **Licence:** free to quote and cite with attribution to feedlab ## Frequently asked questions ### What are unique product identifiers? The values that identify a product independently of who is selling it. In practice that means a GTIN, which is the barcode number assigned by the manufacturer, or the combination of a manufacturer part number and a brand where no GTIN exists. ### Why do channels care about product identifiers? Identification lets the channel attach reviews, specifications and competing offers to the same product, and place your offer among them. Without an identifier your listing is an unknown object that has to be matched on text alone, which is far less reliable. ### What is the difference between GTIN, MPN and SKU? A GTIN is globally unique and identifies the product no matter who sells it. An MPN is assigned by the manufacturer and is only unique within that manufacturer, which is why it needs a brand alongside it. A SKU is a code you invent for your own stock control and means nothing to anyone else. ### What if my products have no identifiers at all? Declare it, by setting identifier_exists to no. That is the correct handling for custom, handmade, vintage and own-brand goods with no manufacturer-assigned identifier. It is not a way to suppress warnings on products that do have barcodes you have not entered. ## Primary sources - [Google: Unique product identifiers](https://support.google.com/merchants/answer/160161)