GTIN, MPN and brand in Merchant Center: how to audit product identifiers properly

GTIN, MPN and brand are often grouped together because Google uses them as unique product identifiers. The operational mistake is to treat them as three interchangeable fields that must always be populated. They are not. Each has a different job, and the correct value comes from the identity of the product, not from a feed optimisation shortcut.

Google's current guidance recommends providing valid identifiers whenever they exist and warns that products with an assigned GTIN may have limited visibility when it is omitted. At the same time, Google explicitly recognises that some products genuinely do not have GTINs. The goal is accuracy, not maximum field population.

Why product identity matters

If two retailers sell the same branded product, the manufacturer's identifiers help platforms recognise that those offers refer to the same underlying item. That supports product matching, richer listings and better understanding of the catalogue. It also gives you a stable way to connect supplier data, ecommerce data and channel data.

Bad identifiers do the opposite. A fabricated GTIN can incorrectly associate a product with something else. Reusing one GTIN across different manufacturer variants can blur distinct products. Using your store name as the brand for a product you did not manufacture can misdescribe the offer.

GTIN: use the manufacturer's number for the exact product

GTIN is the global identifier family that includes familiar formats such as EAN, UPC and ISBN. Google recommends submitting a valid GTIN when one has been assigned by the manufacturer. For widely manufactured products this is one of the strongest pieces of identity data you can provide.

What I check

• Does the supplier/manufacturer provide a GTIN for the item?
• Does the value pass basic format/checksum validation?
• Does it identify the exact size, colour, capacity or other variant?
• Are different variants incorrectly sharing one GTIN?
• Has an internal SKU been accidentally mapped into the GTIN field?
• Are leading zeros being lost by spreadsheets or data types?

That last point is common. Treat identifier values as identifiers, not arithmetic. Spreadsheet formatting and database type choices can alter strings that must remain exact.

Brand: identify the product brand, not the retailer

For branded products, submit the brand that customers recognise as the product's brand. If you manufacture or genuinely own a private-label product, your brand may of course be correct. If you are reselling another manufacturer's product, your store name is not a substitute.

Google's product data specification also gives specific guidance for compatible products: use the brand and GTIN of the manufacturer that actually made the compatible product rather than using the OEM brand simply to indicate compatibility.

MPN: the manufacturer's own part number

MPN is the part number used by the manufacturer to identify a product. In many catalogues it is particularly useful where GTIN coverage is incomplete or where technical products are commonly bought by part number.

Do not confuse MPN with your internal SKU. They may happen to match for private-label products you manufacture, but for a normal branded catalogue the retailer's stock code and the manufacturer's part number are separate concepts.

What if the product genuinely has no GTIN?

Not every product has global identifiers. Google lists examples such as custom-made goods, certain vintage products and some private-label situations. In those cases, the correct answer is not to buy or invent random barcodes simply to fill the field.

The identifier_exists attribute can indicate that standard unique product identifiers are not available. Use it when that is factually true, not when the business simply failed to collect a manufacturer's identifier.

Situation	Better approach	Avoid
Branded product with manufacturer GTIN	Submit the correct GTIN, brand and relevant MPN.	Omitting the GTIN or replacing it with SKU.
Private-label product you own/manufacture	Use your actual brand; use valid assigned GTIN if one exists, plus a meaningful MPN where appropriate.	Inventing a third-party brand or fake GTIN.
Custom / one-off product with no assigned identifiers	Represent the lack of identifiers accurately and use the appropriate identifier_exists behaviour.	Buying an unrelated code just to populate the field.
Compatible accessory	Use the compatible product manufacturer's identity data and express compatibility elsewhere.	Using the OEM brand as if it manufactured the compatible item.

Variants: the exact sellable offer matters

Google's identifier guidance is explicit that variants such as different colours or sizes can require different unique identifiers. Operationally, this is where many catalogues fail because the parent product holds one identifier and every child offer inherits it.

For each sellable variant, ask: what barcode or manufacturer identifier is physically associated with this exact item? If the answer changes by size, colour or capacity, the feed should normally reflect that difference.

Bundles and multipacks need deliberate treatment

Do not assume the GTIN of a single unit describes a retailer-created bundle of several units. Product identity should reflect the offer being sold and the current Google specification. For complex bundles, review the current attribute requirements before submitting identifiers.

A practical identifier audit

A useful data-quality report

For each product family, report: total offers, GTIN coverage, valid format rate, duplicate GTIN rate across non-identical offers, brand completeness, MPN completeness, identifier_exists usage and the source system for each field. That gives developers and merchandising teams something specific to improve.

Common questions