GTINs Explained: When You Need Them and What to Do Without

That last point is why Google and AI agents care. A GTIN tells them the blender on your site and the blender on a marketplace are one item, so they can group offers and compare prices. Google defines it as the same number for the same product from any seller.

Those are the formats on Google's gtin attribute page. Spaces and dashes are ignored, and you can send up to 10 values when an item carries more than one code.

The last digit is a check digit calculated from the others, and Google requires a correct one (test it with the GS1 check digit calculator). We run that calculation over the whole feed before anything ships. A typo in a supplier file looks perfectly normal and fails without warning. Google also rejects codes starting with 2, 02 or 04, which are in-store and variable-weight codes, plus coupon prefixes 05, 98 and 99. If your ERP prints shelf labels starting with 2, keep them out of the feed.

Retailers take the manufacturer's code from the supplier sheet. Brand owners license numbers from their national GS1 office: GS1 US lists a single GTIN at $30 with no renewal, or 100 GTINs for $750 plus $150 a year (as of October 2026).

`brand` is required for any product with a clear brand, including products you make yourself. One value, one language, up to 70 characters. `mpn` is required when there's no manufacturer GTIN. Only invent an MPN if you are the manufacturer. Each color needs its own MPN, while apparel sizes often share one.

`identifier_exists` set to no is meant for custom goods, antiques, vintage items or books published before 1970. Google warns you if it finds evidence an identifier exists.

Here we disagree with a lot of agency playbooks. Setting identifier_exists = no across a catalog makes the "missing identifiers" warnings vanish, so teams love it. It's wrong for any product with a brand. Google's brand page says that if you make and sell an unbranded product, you should use your store name as the brand and send an MPN instead. A clean warning list with wrong data underneath helps nobody.

A typical private-label fix, on a fictional shirt:

The SKU moved from gtin, where it was invalid, to mpn, where Google allows your own code.

Start in Merchant Center under Products, Needs attention, filter by identifier issues, then trace each one back to its source data.

• One GTIN on every variant

  A parent barcode carried down to all sizes. Pull variant-level codes from the supplier

• Scientific notation

  Excel turns a 13-digit EAN into 8.71235E+12. Format the column as text first

• Lost leading zero

  A UPC starting with 0 shrinks to 11 digits. Store GTINs as text

• Internal SKU in gtin

  Your own codes belong in mpn

• In-store prefixes

  Codes starting with 2, 02 or 04 are internal. Remove them

• Feed and page mismatch

  Generate the feed and the PDP markup from the same field

On Shopify, most Google channel setups send the variant's Barcode field as gtin, so fix it there. Some teams keep a supplemental sheet just for identifiers. It works until someone edits the store and forgets the sheet. We prefer one source of truth upstream, as the product feed optimization guide explains. With identifiers clean, the next job is mapping your catalog to Google's product taxonomy, and the Google Merchant Center requirements checklist covers the remaining account and feed basics.