Set identifier_exists to no in Google Merchant Center only when a product genuinely has no GTIN, no MPN and no brand, as with custom, handmade or vintage goods. If the manufacturer assigned a GTIN, submit it in the gtin attribute; if not, submit brand and mpn. Google calls these three attributes unique product identifiers (Google Merchant Center Help, About unique product identifiers).
What unique product identifiers are
Unique product identifiers (UPIs) tell Google exactly which product you are selling. Google Merchant Center uses three (Google Merchant Center Help, About unique product identifiers):
gtin: the Global Trade Item Number, the number encoded in a product's barcode, assigned through GS1.mpn: the manufacturer part number, the manufacturer's own code for the product.brand: the brand name of the product.
As of October 2026, Google's product data specification requires gtin for products with a manufacturer-assigned GTIN, and mpn for products without one (Google Merchant Center Help, Product data specification).
GTIN formats Google accepts
The gtin attribute accepts several GTIN formats (Google Merchant Center Help, GTIN [gtin]):
| Format | Where it is used | Length |
|---|---|---|
| UPC (GTIN-12) | North America | 12 digits; convert 8-digit UPC-E codes to 12 digits |
| EAN (GTIN-13) | Europe | 13 digits |
| JAN (GTIN-13) | Japan | 8 or 13 digits |
| ISBN | Books | 13 digits; convert ISBN-10 to ISBN-13 |
| ITF-14 (GTIN-14) | Multipacks | 14 digits |
Spaces and dashes in a GTIN are accepted but ignored. Google accepts only valid GTINs as defined by GS1, which means the check digit must be correct and restricted or coupon prefixes are rejected. A product with more than one GTIN, such as a UPC and an ISBN-13, can repeat the gtin attribute, up to 10 times (Google Merchant Center Help, GTIN [gtin]).
When to set identifier_exists to no
The identifier_exists attribute tells Google Merchant Center that a product has no unique product identifiers. Google gives two typical cases (Google Merchant Center Help, Identifier exists [identifier_exists]):
- Custom or one-of-a-kind goods, such as custom T-shirts, art and handmade goods.
- Products made before GTINs existed, such as vintage products, antiques and books published before 1970.
Google asks merchants to set identifier_exists to no only when they are certain the product has no assigned identifiers. Values are yes, true, no or false, in English. If you do not submit the attribute, Google treats it as yes (Google Merchant Center Help, Identifier exists [identifier_exists]).
Your own brand and MPN for custom goods
A shop that makes its own products can often avoid identifier_exists altogether. For custom or homemade goods with no official brand, Google suggests using your store name as the brand and an mpn of your choosing that uniquely identifies the product (Google Merchant Center Help, Identifier exists [identifier_exists]).
Keeping identifiers clean in your feed
Most GTIN errors come from data, not from missing products: a placeholder like "N/A", a GTIN stored with a prefix, or a blank value that should simply be left out. Google does not allow placeholder values in gtin or brand, and advises leaving gtin out when you are unsure it is valid (Google Merchant Center Help, Product data specification).
In Product Feed Master, gtin, mpn, brand and identifier_exists are separate fields in the canonical product schema. You can map them from different source columns, clean them with transformation rules such as trim, and correct individual products by hand without the next import overwriting your edit (editing products).
Frequently asked questions
Can I make up a GTIN?
No. A GTIN must be a valid number assigned through GS1, with a correct check digit. If the manufacturer did not assign one, submit brand and mpn instead.
Do books need a GTIN?
Books use their ISBN as the GTIN. Google asks for the 13-digit ISBN; convert older 10-digit ISBNs to ISBN-13.
Should I set identifier_exists to no to avoid GTIN errors?
No. Set identifier_exists to no only when the product truly has no GTIN, MPN or brand. Google says setting it wrongly can cause problems with your products, so fix the identifiers instead.
What is the default value of identifier_exists?
If you do not submit the attribute, Google treats it as yes, meaning it expects identifiers for the product.