Missing or invalid GTIN on Shopify products in Google Merchant Center: what to do

A GTIN is a product's global barcode number: a UPC, EAN, JAN, ISBN or ITF-14. Google uses it to match your listing with the same product elsewhere. Google says products "with missing or incorrect GTIN attributes may have limited visibility", and that if a product has a GTIN and you leave it out, it "could be disapproved" (Google: GTIN).

Who needs one

• Branded products made by someone else almost always have a manufacturer-assigned GTIN. Google recommends sending it.
• Your own brand, handmade, custom or vintage items often have none. Google says: "Some products don't have a GTIN assigned, and so you don't need to submit one." Send brand and mpn instead where you have them (same page; Google: product identifiers).
• Never invent one. Google: "When in doubt don't provide a GTIN (for example, don't guess or make up a value)."

Where it comes from on Shopify

Each variant in the Shopify admin has a Barcode field. Shopify's Google & YouTube app and most feed apps send that field as the GTIN. So the fix for a missing GTIN is usually to fill in the Barcode for each variant, from the manufacturer's packaging or your supplier, not at product level: each size and colour has its own GTIN.

Common mistakes

• Wrong length or check digit. Valid GTINs are 8, 12, 13 or 14 digits, and the last digit is a check digit calculated from the others. A typo or a dropped leading zero makes it invalid.
• The same barcode on several variants. Copying one barcode to every size is common, and wrong.
• Internal codes in the Barcode field. SKUs or warehouse codes aren't GTINs. Google also restricts some prefixes, such as 2, 02 and 04 (reserved for store-internal use) and 05, 98 and 99 (coupons).

Find them by hand (free)

1. In Merchant Center, filter products by identifier issues (for example "Incorrect GTIN", "Invalid value [gtin]" or limited performance due to missing identifiers) and download the list.
2. In Shopify, export your products (Products → Export). The CSV has a Variant Barcode column. Sort it to find blanks and repeated values.
3. Check lengths in the spreadsheet, and test doubtful ones with GS1's free check digit calculator.

Checking the product pages too

Catalog Truth is a free check that reads your store's public product list and up to 20 product pages. On the barcode side it flags GTINs in the page's structured data with the wrong length or check digit, variants that share one GTIN, and pages that carry no GTIN at all. It checks prices, stock and policy pages in the same pass. No sign-up.

Limits

• It sees only what your product pages publish. If your theme doesn't put barcodes in the page, it reports "no GTIN" even when your feed sends them, so treat that warning as "check your feed", not proof.
• It can't tell whether a valid-looking GTIN belongs to the right product. Only GS1 data or the manufacturer can.
• It doesn't log in to Merchant Center and checks up to 20 product pages per scan.